Abstract:
A friction material comprising a filler, a binder, and a lubricant, wherein a part or the whole of the filler is constituted by molybdenum trioxide. Not only is the friction material improved in anti-cracking property and anti-fading property under high-temperature and high-load conditions, but the friction material can be prevented from deterioration due to ashing.

Description:
This application is a continuation of application Ser. No. 08/091,019, filed Jul. 14, 1993, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to friction materials to be used in brakes, clutches, and the like, for cars and industrial machines. 
     2. Description of the Related Art 
     Friction materials of the type comprising a fibrous reinforcement, an inorganic filler, a friction modifier, and a binder, as disclosed in U.S. Pat. No. 4,226,759 and U.S. Pat. No. 4,273,699, for example, are generally limited in use because the conventional friction materials have a tendency to develop cracks or to deteriorate due to ashing when used under high-temperature and high-load conditions. There is a further tendency for a problem that the friction coefficient is lowered at the time of frictional braking (fading phenomenon) because of decomposed gas generated from the binder and organic dust of the friction modifier contained in the friction material. 
     SUMMARY OF THE INVENTION 
     The present invention provides a friction material excellent in prevention of fading due to friction coefficient lowering, development of cracks and deterioration due to ashing. According to the present invention, friction material comprising a fibrous reinforcement, an inorganic filler, a friction modifier, and a binder, is characterized in that the friction material contains molybdenum trioxide in the filler. Lowering of friction coefficient, generation of cracks and deterioration due to ashing can be prevented by mixing molybdenum trioxide in the friction material even in applications where the friction material is used under high-temperature and high-load conditions. If the molybdenum trioxide content is less than 0.5%, the effect is not sufficient to the intended friction material characteristics. As the molybdenum trioxide content increases to 15% from 0.5%, the effect increases in accordance with the content. If the molybdenum trioxide content is more than 15%, the effect does not increase further. Accordingly, the molybdenum trioxide content is preferably selected to be in a range of from 0.5% to 15%. 
     Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     To produce a friction material of the present invention, for example, a mixed and stirred compounding raw materials containing molybdenum trioxide, as shown in Table 1, is preformed under surface pressure in a range of from 100 to 500 kgf/cm 2 , the preformed material is introduced into a hot press having a pressure plate set therein, and subjected to thermal forming at a temperature in a range of from 130 to 180° C. under surface pressure in a range of from 200 to 1000 kgf/cm 2  for a time period in a range of from 3 to 15 minutes, thereby to finish up a material having a predetermined thickness and a predetermined density. Then, the finished material is subjected to heat treatment at a temperature in a range of from 150 to 300° C. for a time period in a range of from 1 to 15 hours. Then shaping treatment is performed to obtain a desired brake pad. 
     
                       TABLE 1______________________________________                      Mixture                      WeightRaw Materials              Proportion______________________________________Fibrous Aramid fiber such as KEVLAR, etc.,                            2-70Reinforce   inorganic fiber such as ceramic fiber, rockment    wool, etc., metallic fiber such as steel   fiber, copper fiber, brass fiber, etc.Inorganic   Metal oxide such as alumina, silica, etc.,                            6-70Filler  solid lubricant such as graphite,   molybdenum disulfide, etc., and barium   sulfate.   Molybdenum trioxide    0.5-15Friction   Metal particles such as copper particles,                          0.5-10Modifier   brass particles, etc.   Organic dust such as rubber dust, cashew                            1-15   dust, etc., and inorganic matter such as   vermiculite, etc.Binder  Thermosetting resin such as phenolic resin,                            5-15   etc.______________________________________ 
    
     Illustrative examples of the present invention will be described below. 
     Raw materials for friction materials having compositions shown in Table 2 were treated in accordance with the above-mentioned production procedure to prepare friction materials 1 and 2 of the present invention and a comparative friction material. 
     
                       TABLE 2______________________________________       Mixture Weight Proportion         Friction   Friction         Material 1 Material 2                             Comparative         of the     of the   FrictionRaw Material  Invention  Invention                             Material______________________________________KEVLAR (E. I. Du-Pont)          5          5        5copper fiber  13         13       13ceramic fiber 15         15       15ceramic particles          5          5        5graphite      10         10       10barium sulfate         28         25       30molybdenum trioxide          2          5       --copper particles          2          2        2rubber particles          5          5        5cashew dust    5          5        5phenolic resin         10         10       10______________________________________ 
    
     These friction materials were subjected to evaluation test by using a full-size dynamometer. The sizes of test articles used therein were selected as follows: pressure plate of 5 mm thickness; friction material of 10 mm thickness; and friction area of 45 cm 2 . Conditions of bench test were selected as follows: JASO fading test: speed 100 km/hr→0 km/hr, deceleration 0.45 G, braking interval 35 sec×10 times; disc rotor: ventilated disc rotor with a thickness of 18 mm, a rotor radius of 0.100 m and a tire radius of 0.280 m. Results of the test were as shown in Table 3. 
     
                       TABLE 3______________________________________        Friction   Friction        Material 1 Material 2                            Comparative        of the     of the   FrictionItem         Invention  Invention                            Material______________________________________Fading Minimum μ        0.150      0.180    0.130Cracking     .increment.                   ∘                            xAshing deterioration        ∘                   ∘                            x______________________________________ 
    
     In the above table, &#34;fading minimum μ represents the minimum friction coefficient in the fading test (10 braking times). In the above table, the symbol ∘ indicates that there is no problem with cracking or ashing deterioration, the symbol Δ indicates that these characteristics respectively are in an allowable range, and the symbol x indicates the existence of a problem. 
     As shown in the above table, not only are the friction materials of the present invention both higher in the minimum friction coefficient than the comparative friction material, but also, the friction materials of the present invention are in an allowable range for generation of cracks and further, are free from deterioration due to ashing. 
     As described above, according to the present invention, there are remarkable effects in improved anti-cracking properties of the friction material under high-temperature and high-load conditions, improved prevention of deterioration due to ashing, and improved anti-fading properties due to reduction of gas generation from components of the friction material. 
     Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.