Method for the preparation of friction material, specifically for the manufacture of brake pads and associated brake pads

A method for obtaining an inorganic binder for friction material without asbestos and insensitive to heat degradation during use, the method comprising:

• obtaining a basic aqueous solution, at a pre-fixed pH, of an alkaline silicate and a hydroxide in water through dissolving, in water, an alkaline silicate powder of sodium or potassium;
• mixing the aqueous solution of hydroxide and alkaline silicate with a material selected from a group consisting of metakaolin, kaolin, fly ash, and mixtures of thereof until a wet paste is obtained;
• forming and drying the wet paste under atmospheric pressure until a dried geopolymer aggregate is synthesized, wherein a final moisture content of the dried geopolymer aggregate is less than 30% in weight calculated on the total weight of the geopolymer binder after drying;
• and
• grinding the dried geopolymer aggregate to a powder, wherein the ground dried geopolymer aggregate constitutes the inorganic binder.

An inorganic binder for friction materials without asbestos and insensitive to heat degradation during use, the inorganic binder comprising:

• a hydroxide and an alkaline silicate dissolved, in water, an alkaline silicate powder of sodium or potassium and mixed with a material selected from a group consisting of metakaolin, kaolin, fly ash, and mixtures of thereof until a wet paste is obtained, wherein the wet paste is formed and dried under atmospheric pressure until a dried geopolymer aggregate is synthesized and ground into a powder, wherein the inorganic binder has:
• a moisture content less than 30% in weight;
• an Si/Al molar ratio between 1.5-6;
• a granulometry of less than 800 microns;
• an alkaline hydroxide content in the mixing stage between 0 and 10%;
• a FTIR spectrum with peak associated with a symmetrical vibration of the Si—O bond which moves from its initial position of 1038 cm−1 for metakaolin to a value of less than 1000 cm−1 for the geopolymer obtained after the mixing stages with the silicate and alkaline hydroxide solution and drying;
• an amorphous structure after the synthesis stage;
• the ability to reconsolidate if exposed to pressure and temperature between 150 and 2000 kg/cm2 and 100-250° C.;
• and
• a reconsolidation mechanism of the geopolymer powder for temperature and pressure conditions similar to those normally used in the production of brake pads;
• and
• wherein the inorganic binder maintains its amorphous structure after the consolidation stage.

A brake pad with a block of non-asbestos friction material comprising:

• inorganic and/or organic and/or metallic fibers;
• at least one filler or abrasive;
• at least one friction modifier or lubricant;
• and
• at least one binder, wherein the at least one binder is
• almost completely or completely and exclusively inorganic,
• made up at least 90% of an amorphous geopolymer or a mixture of amorphous geopolymers, and
• obtained through
• obtaining a basic aqueous solution, at a pre-fixed pH, of an alkaline silicate and a hydroxide in water through dissolving, in water, an alkaline silicate powder of sodium or potassium;
• mixing the aqueous solution of hydroxide and alkaline silicate with a material selected from a group consisting of metakaolin, kaolin, fly ash, and mixtures of thereof until a wet paste is obtained;
• forming and drying the wet paste until a dried geopolymer aggregate is obtained, wherein a final moisture content of the wet paste is less than 30% in weight calculated on the total weight of the geopolymer binder after drying;
• grinding the dried geopolymer aggregate to a powder;
• mixing the ground dried aggregate as an inorganic binder with inorganic and/or organic and/or metallic fibers, at least one friction modifier or lubricant, and at least one filler or abrasive into a friction material compound to obtain a raw frictional material compound having as binder the ground dried geopolymeric aggregate;
• and
• hot molding between about 40° C. and about 300° ° C. the raw frictional material compound under pressure greater than a water saturation pressure at the molding temperature to obtain a block of friction material having at least 90% geopolymer as binder.