Abstract:
A non-asbestos friction material containing friction dust comprising a composite of inorganic compound with polymerization product of cashew nut shell oil is disclosed. The material is used for the brake lining, disc pad and clutch facing for cars and industrial machinery.

Description:
This application is a continuation of application Ser. No. 07/784,583 , filed on Oct. 29, 1991, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a non-asbestos friction material used for the brake lining, disc pad, clutch facing, etc. for cars and industrial machinery. 
     In said friction material for cars and industrial machinery, solid lubricant is usually formulated in consideration of the stability of friction coefficient and the wear resistance. As these solid lubricants, organic friction dust and inorganic lubricants such as graphite and molybdenum disulfide have been used so far. 
     For this organic friction dust, it is common to use particles obtainable by polymerizing cashew nut shell oil and particles obtainable by vulcanizing elastic polymers such as rubber. By mixing these with friction material, adequate elasticity is given to the friction material and, as a result, the friction characteristics are stabilized, since the contact area of friction surfaces increases through the elastic deformation on engaging with partner component of friction. Namely, the action of this organic friction dust is considered that, through the fluid or gas lubrication by low-molecular organic ingredients produced by depolymerization due to the frictional heat, the friction characteristics at low temperature is stabilized. 
     There is a problem, however, that, since the thermal decomposition products become too much and the lubrication becomes excessive at high temperature, so-called fade phenomenon, the friction coefficient being abruptly decreased, is caused resulting in an increased wear, too. Namely, the defect of the organic friction dust of this type lies in only the fade phenomenon, thus, with the friction materials put now into practice, the fade phenomenon and the wear at high temperature are suppressed as low as possible in consideration of the stability of friction characteristics to realize on a balance of both. 
     In practice, however, there has been a limit for this as long as the organic friction dust is used. 
     As a result of extensive investigations in view of this situation, a non-asbestos friction material, with which said problem is solved, has been developed according to the invention. 
     SUMMARY OF THE INVENTION 
     The invention is characterized by providing a non-asbestos friction material containing a composite of stratified inorganic compound or fibrous inorganic compound with polymerization product of cashew nut shell oil. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a chart showing results of the fade test of the inventive friction materials and the conventional friction material. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As described, by making the polymerization product of cashew nut shell oil as an organic friction dust a composite with inorganic compound, the proportion of organic ingredient decreases, thereby the amount of decomposed gas at high temperature decreases to improve the fade phenomenon. 
     Yet, though the reason is not evident, stratified foamed material such as vermiculite is more effective as a stratified inorganic compound and ceramic wool such as slag wool and calcium carbonate whisker etc. are more effective as fibrous inorganic compounds. The polymerization product of cashew nut shell oil is effective within a range of 5 to 95% and the stratified inorganic compound or fibrous inorganic compound within a range of 95 to 5%. The optimal level is 40 to 95% for the polymerization product of cashew nut shell oil and 60 to 5% for ths stratified inorganic compound or fibrous inorganic compound. 
     In following, the invention will be illustrated based on the examples. 
     EXAMPLE 
     The polymerization product of cashew nut shell oil and the slag wool, calcium carbonate whisker or vermiculite as a fibrous inorganic compound or stratified inorganic compound were mixed at weight ratios shown in Table 1. Further, after 10% curing agent such as hexamine or furfural to the weight of polymerization product of cashew nut shell oil were added to each mixture, the whole was heated to cure. Thereafter, this cured product was pulverized to a fixed particle size with pulverizer to obtain composite dusts A through F. 
     Next, as shown in Table 2, these composite dusts A through F were formulated with other materials to make the inventive friction materials 1 through 6 according to the usual method. It is only necessary to formulate these composite dusts to friction materials in amounts of 3 to 30 wt. %, preferably 5 to 20 wt. %. Besides, for comparison, the conventional friction material 7 formulated with conventional resin dust in place of said composite dusts was also prepared. 
     
                       TABLE 1______________________________________Composite dust  A     B      C    D    E    F______________________________________Polymerization product of           70    50     70   50   70   50cashew nut shell oilSlag wool       30    50     --   --   --   --Vermiculite     --    --     30   50   --   --Calcium carbonate whisker           --    --     --   --   30   50______________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________  Inventive       Inventive            Inventive                 Inventive                      Inventive                           Inventive                                ConventionalFormulating  friction       friction            friction                 friction                      friction                           friction                                frictionmaterial  1    2    3    4    5    6    7__________________________________________________________________________Composite  A, 15       B, 15            C, 15                 D, 15                      E, 15                           F, 15                                --dustPhenol resin  13   Same as            Same as                 Same as                      Same as                           Same as                                Same as       left left left left left leftResin dust  --   --   --   --   --   --   15Barium 30   Same as            Same as                 Same as                      Same as                           Same as                                Same as       left left left left left leftCopper 10   Same as            Same as                 Same as                      Same as                           Same as                                Same aspowder      left left left left left leftGraphite  15   Same as            Same as                 Same as                      Same as                           Same as                                Same as       left left left left left leftCeramic   2   Same as            Same as                 Same as                      Same as                           Same as                                Same as       left left left left left leftAramid fibers   5   Same as            Same as                 Same as                      Same as                           Same as                                Same as       left left left left left leftPotassium  10   Same as            Same as                 Same as                      Same as                           Same as                                Same astitanate    left left left left left leftfibers__________________________________________________________________________ Figures indicate % by weight. 
    
     Of said respective friction materials, change in friction coefficient as a function of the number of brakings was examined using full-size dynamometer for the fade test according to JASO, the results of which are shown in FIG. 1. Moreover, of said friction materials, the wear test by temperature was carried out under the condition of N=1000 stop and the friction coefficient and the wear level were measured. Results are shown in Table 3. 
     
                                           TABLE 3__________________________________________________________________________     Friction materialTemper-     Inventive          Inventive               Inventive                    Inventive                         Inventive                              Inventive                                   Conventialature     friction          friction               friction                    friction                         friction                              friction                                   frictionItem °C.     1    2    3    4    5    6    7__________________________________________________________________________Wear 100  0.12 0.10 0.13 0.10 0.12 0.10 0.15level300  0.22 0.25 0.23 0.28 0.30 0.27 0.40μm500  0.55 0.77 0.62 0.89 0.90 0.80 1.13Friction100  0.40 0.41 0.39 0.39 0.39 0.41 0.40coef-300  0.38 0.39 0.39 0.38 0.37 0.39 0.35ficient500  0.35 0.37 0.36 0.38 0.37 0.35 0.32__________________________________________________________________________ 
    
     As evident from FIG. 1, it can be seen that all of the inventive friction materials 1 through 6 (line segments 1 through 3 in diagram) have the minimum friction coefficient at the time of fade being higher by 0.05 to 0.1 than that of the conventional friction material 7 (line segment 4 in diagram). Moreover, from Table 3, it is seen that the inventive friction materials show decreased wear and increased friction coefficient at high temperatures of 300° C. and 500° C. in all cases. 
     As described, in accordance with the invention, composite dust provided with both elasticity and adequate lubrication was obtained by compositing the organic friction dust with inorganic material. The invention therefore exerts conspicuous effect to provide the nonasbestos friction material with which the problem of balance between fade phenomenon and high-temperature wear on braking of cars etc. was solved at a stroke.