Friction material compositions and related friction elements

Abstract

An asbestos-free friction material composition and related brake pads for vehicles, comprising organic and / or inorganic and / or metallic fibers, at least a binder, at least a friction modifier or lubricant, at least a filler or abrasive, and at least soluble salts of barium and / or calcium and / or aluminum and / or silver in a proportion of between 0.5 and 10% by weight, of which barium carbonate, calcium hydroxide, aluminum triacetate, and silver acetate are preferred.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This patent application claims priority to Italian Patent Application No. 102022000023835, filed November 18, 2022, the entire disclosure of which is incorporated herein by reference.

[0002] [Technical field] The present invention relates to friction material compositions that are particularly suitable for the manufacture of friction layers / blocks for friction elements, such as, for example, braking elements incorporated into vehicle braking systems.

[0003] The present invention also relates to related friction elements, such as brake pads or brake shoes for vehicles, made with the friction material composition.

[0004] The friction material composition of the present invention does not contain asbestos and belongs to the so-called NAO ("Non-Asbestos Organic") type, and in particular, but not exclusively, does not contain copper. [Background technology]

[0005] Friction materials that do not contain asbestos fibers and are intended for use in vehicle brake pads / shoes contain five classes of ingredients: fibrous materials composed of inorganic and / or organic and / or metallic fibers, binders, fillers, one or more lubricants or friction modifiers, and one or more abrasives.

[0006] Fibrous materials that replace asbestos can be both inorganic, such as rock fiber or rock wool, wollastonite, and glass fiber, and organic, such as aramid fiber and carbon fiber, or metallic, such as steel fiber. Binders are typically thermosetting polymers, such as those based on phenolic resins. Various materials are used as fillers to provide sufficient strength to the friction material, such as barium sulfate (barium sulfate), calcium carbonate, talc, magnesium oxide, and vermiculite. Zirconium silicate, zirconium oxide, alumina, silicon carbide, and mica are commonly used as abrasives. Metal sulfides, such as molybdenum disulfide, iron sulfide, copper, and tin, graphite, and / or coke can be used as friction modifiers. Other classes of materials can also be added in smaller proportions, such as powdered or granular rubber, "friction dust" (well-known materials readily available on the market), and other organic materials.

[0007] However, vehicle brake pads / shoes made from the above-mentioned friction materials are not without drawbacks.

[0008] In particular, they can release ions into the environment upon contact with water, which is common for vehicle components assembled on or near vehicle wheels. In particular, known friction materials can release free ions as sulfates, sulfites, oxalates, and phosphates when in the presence of water / moisture.

[0009] Such emissions can be a major drawback: firstly, the release of these types of ions into the environment can cause pollution, and secondly, as such ions are released close to the brake discs, they can be a major cause of corrosion of the disc material, which is usually made of steel or cast iron.

[0010] The release of soluble sulfate ions from brake pads, for example, when they come into contact with ferrous materials, causes the formation of so-called "green rust" [Fe4 2+ Fe2 3+ (HO - )12 ] 2+ *[SO4 2- ·2H2O] 2- Green rust compounds are thought to be intermediates in the oxidative corrosion of iron, forming iron(III) oxyhydroxides (so-called "brown rust").

[0011] To date, there is no known solution for eliminating the release of ions, such as sulfates, from brake pads / shoes unless the source of those ions is eliminated from the friction material formulation. For example, the release of sulfate ions can be eliminated by eliminating the use of sulfides in the friction material formulation. However, this solution is impractical because the elimination of sulfides would have a significant adverse effect on the tribological properties of the final product, e.g., the friction material blocks present on the brake pads / shoes.

[0012] US2015192182A1 discloses the use of modified activated carbon in brake pad formulations, which should be able to adsorb sulfate ions in solution before they can chemically attack the iron material of the brake disc. However, this solution has proven to be not entirely reliable, and is complex and expensive to implement, as both the activated carbon used as the adsorbent and the phenolic resin used as the binder must be chemically modified to become hydrophilic. Summary of the Invention

[0013] An object of the present invention is to develop a novel asbestos-free friction material composition that can overcome the drawbacks of the prior art.

[0014] In particular, the presently disclosed subject matter contemplates providing an asbestos-free friction material composition that maintains all the usual ingredients to have predictable braking performance, but that is substantially unaffected by the ion-release phenomenon when exposed to water or moisture.

[0015] It is therefore a further object of the present invention to provide an associated brake element, in particular a brake pad or brake shoe, comprising a friction material composition which, during use, makes it possible to avoid or at least strongly reduce surface corrosion of a friction partner cooperating therewith, such as a brake disc or brake drum.

[0016] Accordingly, the present invention relates to a friction material composition and related braking elements as defined in the appended claims.

[0017] According to the present disclosure, for any friction material composition known to be subject to the ion-release phenomenon, a certain amount of a water-soluble compound of a specifically selected metal is added to the friction material standard composition itself to obtain a modified friction material composition that, when molded into a friction material block that is assembled to form a braking element such as a brake pad or shoe, maintains all the chemical and physical properties of the corresponding standard composition, thus ensuring fully predictable braking performance, while avoiding or strongly reducing surface corrosion of its friction partner, because the added metal compound is selected to chemically react with the ions ultimately released by / in the composition and form a water-insoluble salt of such metal and ion directly in / on the friction material block. In this way, the released ions cannot reach and attack the ferrous material of the friction partner.

[0018] Accordingly, the present disclosure relates to an asbestos-free friction material composition belonging to the class of friction materials known as NAO (non-asbestos organic), comprising as raw ingredients at least a fibrous material, at least one filler, at least one binder, at least one lubricant and / or other friction modifier (preferably two or more lubricants and / or friction modifiers), and at least one abrasive, and further comprising at least one water-soluble compound of a metal capable of reacting (e.g., by an exchange reaction) with an anion normally present in / that may be released by one or more of the aforementioned raw ingredients to form a water-insoluble salt of the metal and ion therewith.

[0019] With respect to corresponding known NAO friction compositions (i.e., having the same component materials in substantially the same amounts for all of the above known general classes of materials), the friction material composition of the present invention therefore further comprises a specific amount of a water-soluble compound of a metal selected from among metals that are capable of forming a water-insoluble salt with releasable ions from / within the friction material composition itself in the presence of water and / or moisture.

[0020] In other words, the present invention resides in adding to (any) standard friction material composition one or more metal salts and / or hydroxides that are readily soluble in water and at the same time capable of forming water-insoluble salts with sulfate, sulfite, oxalate, and phosphate ions normally present in, and / or, as the case may be, released by, the friction material composition.

[0021] Here and hereinafter, "easily soluble" in water means 1*10 as specified in Clark, Roy W.; Bonicamp, Judith M. "Solubility and Solubility Products." J. Chem. Educ. 2000 77 1558. -9 Higher solubility product constant, i.e., K psIn particular, the solubility of the cation should be higher than that of sulfate ion for the same cation and in the same solution.

[0022] According to a preferred embodiment, the asbestos-free friction material composition of the present disclosure includes at least one water-soluble compound of barium and / or calcium and / or aluminum and / or silver, such as barium carbonate, calcium hydroxide, aluminum triacetate, and silver acetate.

[0023] Such metal compounds have indeed been found to have the ability to act as scavengers for any of the different ions that may be released from the friction material.

[0024] According to the most preferred embodiment, barium carbonate is used in the asbestos-free friction material composition of the present invention as an additional component to be added to any known friction material composition, because barium contained in BaCO forms an insoluble salt with any of sulfate, oxalate, and phosphate, and can precipitate as BaSO, Ba(PO), BaCO, and BaCrO. Also, barium carbonate is a safe material that is easily available and inexpensive.

[0025] From the above, the present disclosure also relates to a brake element for a vehicle comprising a metal support and a layer or block of friction material carried by the support, wherein the block of friction material is made from the asbestos-free friction material composition of the present invention as disclosed above and is preferably molded onto a first surface of the support, and the block of friction material is configured to capture / isolate and retain any ions, possibly released by one or more of the component materials of the friction material composition during use, in the form of water-insoluble metal salts within or on the friction material, without the ions being able to reach a friction partner of the block of friction material, e.g., a brake disc, and possibly causing chemical etching of the iron material therein.

[0026] The braking element according to the present disclosure is a brake pad or brake shoe for a vehicle.

[0027] The present disclosure also extends to a braking system comprising a braked member constituted by a brake disc or brake drum made of cast iron or steel and at least one braking member constituted by a brake pad or brake shoe adapted to frictionally cooperate with the braked member, the braking member having a friction layer intended to cooperate with the braked member made of the friction material composition of the present invention as disclosed above.

[0028] Further features and advantages of the disclosed subject matter, whether explicitly mentioned or not, will become apparent in light of the disclosure provided below, including practical and comparative non-limiting examples that disclose different possible and non-limiting embodiments thereof, and with reference to the accompanying drawings. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 shows diagrammatically the results given in the first most important section of the AK-Master test carried out on brake pads made with the test friction material according to the invention. [Figure 2] FIG. 2 shows a schematic representation of the same first section of the same AK-Master test as FIG. 1, but performed on brake pads made with the reference friction material. [Figure 3] FIG. 3 shows diagrammatically the results given in the FADE section of the same AK-Master test as in FIG. 1, obtained with brake pads made with the test friction material according to the invention. [Figure 4] FIG. 4 shows diagrammatically the results given in the FADE section of the same AK-Master test as in FIG. 2, obtained with brake pads made with the reference friction material. DETAILED DESCRIPTION OF THE INVENTION

[0030] More specifically, the disclosed asbestos-free friction material composition includes at least one filler, at least fibrous material, at least one binder, at least one lubricant or friction modifier, and at least one or more abrasives according to any of the well-known formulations of friction material compositions commonly used or commercially available to realize braking elements such as brake pads or brake shoes.

[0031] In accordance with one aspect of the present invention, in addition to the standard ingredients described above, the disclosed friction material composition includes at least one water-soluble compound of a metal that is capable, in the presence of water and / or moisture, of chemically reacting with any of the ions (anions) optionally released / releasable by any of the other aforementioned standard raw ingredients present in the friction material composition itself to form a water-insoluble metal salt with such ions, so that these ions can remain trapped / sequestered within the friction material block formed with the presently disclosed friction material composition during use without potentially reaching the friction partner of the friction material block (e.g., a brake disc) and potentially causing chemical etching of the iron material therein.

[0032] In particular, to avoid / strongly limit the ion release phenomenon, the water-soluble compounds of the aforementioned metals to be added to any standard friction material composition are comprised of one or more metal salts and / or hydroxides that are readily soluble in water and, at the same time, capable of forming water-insoluble salts with sulfate, sulfite, oxalate, and phosphate ions normally present in, and / or, as the case may be, released by, the friction material composition.

[0033] Preferably, the asbestos-free friction material composition of the present disclosure includes, in addition to other standard components of friction materials, at least one water-soluble compound of barium and / or calcium and / or aluminum and / or silver, such as barium carbonate, calcium hydroxide, aluminum triacetate, and silver acetate.

[0034] More preferably, the asbestos-free friction material composition of the present disclosure contains a specified amount of barium carbonate in addition to other standard ingredients of commonly used friction materials.

[0035] At least one water-soluble compound of a metal that can chemically react in the presence of water and / or moisture with any of the ions (anions) optionally released / releasable by any of the standard raw ingredients present in the friction material composition to form a water-insoluble metal salt with such ions is present in the friction material composition of the present invention in an amount comprised between 0.5% and 10% by weight, inclusive of the extremes of the interval, calculated on the total weight of the friction material composition.

[0036] Preferably, the friction material composition of the present invention contains 0.5 to 5 wt. % barium carbonate BaCO3 in addition to the standard raw ingredients of NAO friction material.

[0037] Most preferably, the friction material composition according to the present invention contains about 1 wt. % barium carbonate BaCO3 in addition to the standard raw ingredients of NAO friction material.

[0038] In order to obtain the favorable effect of sequestration of the optionally released ions in the friction material composition, it is important that the one or more metal salts and / or hydroxides, which are readily soluble in water and at the same time capable of forming water-insoluble salts with sulfate ions, sulfite ions, oxalate ions, and phosphate ions, have a specific particle size distribution, and therefore a specific surface area, that promotes the chemical reaction of sequestration of the released ions.

[0039] Thus, in a preferred embodiment, the friction material of the present invention may comprise barium carbonate in an amount comprised between 0.5 and 1% by weight and having a particle size distribution between 5 and 80 μm (microns).

[0040] In any case, the one or more metal salts and / or hydroxides that are readily soluble in water and at the same time capable of forming water-insoluble salts with the sulfate, sulfite, oxalate, and phosphate ions contained in the friction material composition of the present invention must have a particle size distribution of less than 100 μm (microns).

[0041] Experimental testing has indeed demonstrated that particle size distributions outside the above ranges, particularly those above 100 microns, adversely affect the solubility of the metal salts and / or hydroxides, thus rendering them less effective.

[0042] Other than the one or more metal salts and / or hydroxides described above that are readily soluble in water and capable of simultaneously forming water-insoluble salts with sulfate, sulfite, oxalate, and phosphate ions, the raw material ingredients of the friction material according to the present invention can be any of the raw material ingredients commonly used in friction materials known in the art.

[0043] In particular, the at least one fibrous material may be selected from the group consisting of inorganic fibers, organic fibers, metallic fibers, and any combination thereof.

[0044] Preferably, the at least one fibrous material is composed of organic fibers selected from the group consisting of polyacrylic fibers, polyaramid fibers, aramid fibers, cellulosic fibers, and mixtures thereof.

[0045] Organic fibers may be included in the friction material composition of the present disclosure, preferably, but not exclusively, as part of the organic binder, since they may have the primary purpose of increasing the strength of the brake pad / shoe that may be made from the friction material composition of the present disclosure under operational working conditions.

[0046] The at least one binder is preferably an organic binder and may be selected from the group consisting of phenolic resin, epoxy resin, silicone resin, modified phenolic resin, melamine resin, polyimide resin, and mixtures thereof.

[0047] The at least one lubricant or friction modifier may comprise, but is not limited to, a sulfide-based lubricant preferably selected from the group consisting of metal sulfides of Sn, Zn, Fe, Mo, and mixtures thereof.

[0048] Many materials can be used as organic or inorganic fillers. Preferably, at least one filler is an inorganic filler selected from the group consisting of mineral fibers, glass fibers, rockwood, phyllosilicates (mica, vermiculite, talc, etc.), titanates, inorganic hydroxides of calcium, magnesium, potassium, and any mixtures thereof.

[0049] The at least one abrasive includes at least one soft / weak abrasive having a Mohs hardness of less than 7 and between 1 and 3, at least one medium abrasive having a Mohs hardness of less than 7 and between 4 and 6, and at least one hard / strong abrasive having a Mohs hardness of 7 or greater, generally between 7 and 9.

[0050] The hard abrasive (i.e., having a Mohs hardness of 7 or greater) preferably, but not exclusively, has a rounded shape and in any event is preferably, but not exclusively, selected from the group consisting of silicon carbide, zirconium sand, zirconium silicate, zirconium oxide, corundum, alumina, mullite, tungsten carbide, zirconium carbide, boron nitride, and any mixture thereof.

[0051] The medium abrasive (i.e., having a Mohs hardness comprised between 4 and 6) is preferably, but not limited to, selected from the group consisting of barium sulfate, magnesium oxide, calcium fluoride, calcium carbonate, wollastonite, calcium silicate, iron oxide, silica, chromite, zinc oxide, and any mixture thereof.

[0052] The soft / weak abrasive (i.e., having a Mohs hardness between 1 and 3) may be selected from, but is not limited to, the group consisting of talc, calcium hydroxide, potassium titanate, mica, zinc oxide, tin oxide, silicates, fluorides, and any mixture thereof.

[0053] In accordance with a preferred embodiment of the present invention, the disclosed friction composition may contain at least one metal or mixture of metals, but is copper-free.

[0054] Here and below, the expression "copper-free" should be understood to imply a copper content and / or a content of copper-containing materials, such as copper alloys, of less than or equal to 0.5% by weight.

[0055] The at least one metal or mixture of metals, when present in the disclosed friction material composition, is not comprised of copper and / or any copper alloy, but is selected from the group consisting of iron, steel, stainless steel, tin, zinc, and any alloy thereof in powder or fiber form.

[0056] Additionally, the disclosed friction material composition may include organic additives selected from the group consisting of polytetrafluoroethylene, friction dust, cashew dust, rubber (ie, NBR, silicone, SBR, etc.).

[0057] Additionally, the disclosed friction material compositions may include carbonaceous materials such as carbon, carbon black, coke, graphite, and mixtures thereof.

[0058] In a further embodiment of the present invention, the average friction material composition disclosed is as follows (% are by weight): Abrasive: Mohs 7-9 08-15% Abrasive: Mohs 4-6 05-15% Abrasive: Mohs 1-3 20-30% Binder (resin) 10-20% Organic additives 08~15% Fiber 03~10% Lubricant 02~08% Carbon 05-15% Barium carbonate (5-80 μm) 0.5-10%

[0059] Finally, the present invention also extends to a braking element, in particular a brake pad or shoe, presenting a layer or block of friction material made from the above-described friction material composition in any known and conventional manner, for example by molding.

[0060] The invention also extends to a braking system comprising a braked member constituted by a brake disc or brake drum made of cast iron or steel and at least one braking element constituted by a brake pad or shoe designed to cooperate by friction with the braked member, the braking member presenting a friction layer or block intended to cooperate with the braked member and made of the friction material composition described above.

[0061] Exemplary Modes of Implementing the Teachings of the Disclosure The inventive and comparative examples are reported herein for illustrative purposes and are not intended to limit the invention.

[0062] Example 1: Several samples of friction material compounds of different chemical compositions and corresponding reference samples were prepared according to different known NAO standard compositions in percentage proportions (by weight) reported in Table 1.

[0063] [Table 1]

[0064] All reference samples have the same chemical composition as the corresponding test samples, except for the missing barium carbonate.

[0065] The ingredients shown in Table 1 were mixed uniformly in a horizontal mixer (e.g., a Loedige-type mixer), molded in a mold onto identical metal flat substrates, and then cured in a conventional manner to form brake pads that were identical except for the chemical composition of the friction material.

[0066] In particular, the pressure applied to the brake pads is 150 to 1800 kg / cm at a temperature of 60 to 200°C. 2 for a duration of 3 to 10 minutes at a pressure of 150 to 500 kg / cm at a temperature of 130 to 180 °C or otherwise preform the mixture in a mold. 2 The pressure was applied for a duration of 3 to 10 minutes.

[0067] Each resulting pressed article was typically post-cured by heat treatment at 150-400°C for a duration of 10 minutes to 10 hours, then spray or powder coated and kiln dried to produce the final product.

[0068] Example 2: Sulfate Release Test The brake pads obtained in Example 1 were each individually subjected to a sulfate release test.

[0069] The test procedure is as follows: Collect 4g of friction material powder; · Boil the collected friction material powder in 100ml of water at 90℃ in a closed system for 8 hours; · Transfer the resulting solution into a 100 ml cylinder and make up to 100 ml with distilled water; ·Perform standard SO4 chromatographic analysis of the diluted solution thus obtained.

[0070] The measurements of the sulfate release tests carried out on all the prepared samples (test and reference) gave average values ​​as reported in Table 2 below.

[0071] [Table 2]

[0072] As is readily apparent from Table 2, the addition of barium carbonate within the ranges shown in Table 1 consistently resulted in a dramatic reduction (20-fold or more) in sulfate ion release from the tested friction material blocks, regardless of compositional variations within the ranges shown in Table 1, apparently due to chemical sequestration of sulfate ions by the barium carbonate salt, which converts itself to Ba(SO), which is a water-insoluble salt and remains trapped in the friction material block instead of being released into aqueous solution.

[0073] In addition, chemical analysis of the friction material powder after the emission test showed that barium from BaCO3 formed insoluble salts with either sulfate, oxalate, or phosphate, and precipitated as BaSO4, Ba3(PO4)2, BaC2O4, and BaCrO4.

[0074] Example 3: Conducting as described in Examples 1 and 2, several identical test friction material compositions and one reference composition were prepared by replacing barium carbonate in the test samples with calcium hydroxide Ca(OH), aluminum triacetate Al(CHCOO), and silver acetate CHCOOAg, respectively, according to the average values ​​of the content ranges shown in Table 1.

[0075] The ion release test was then carried out on the test and reference samples obtained by carrying out the same method as described in Example 2, but with different ions in aqueous solution, namely (PO4)2 3- , SO4 2- and Cl - The concentration of was investigated.

[0076] Again, the final results showed a reduction in the release of these ions of over 10-15 fold relative to the reference sample.

[0077] Chemical analysis of the residual friction material powder after the emission test showed the following: Calcium hydroxide, Ca(OH)2, leads to the precipitation of Ca3(PO4)2 and CaSO3. Aluminum triacetate Al(CH3COO)3 reduces the release of phosphate and forms insoluble AlPO4. ·Silver acetate CH3COOAg results in precipitation of AgCl, Ag3PO4, and Ag2SO3.

[0078] From the above, it can be seen that all the metal compounds tested were equally effective in dramatically reducing the ion release phenomenon in the standard NAO friction material composition.

[0079] Example 4: Four friction material samples were prepared using the same average values ​​of each component shown in Table 1 and with reference to the ranges shown in Table 1, but using different contents (wt%) of barium carbonate, namely: 0.5%, 1%, 2%, and 5%, to confirm the effect of barium concentration on scavenging sulfate ions.

[0080] After obtaining the sample brake pads as described in Example 1 and after carrying out the release test as described in Example 2, the SO4 concentration in the residual aqueous solution was measured. The results obtained are reported in Table 3 below.

[0081] [Table 3]

[0082] As can be seen, the addition of BaCO3 in the NAO friction material composition consistently and dramatically reduces the amount of sulfate ions released at all concentrations of barium carbonate.

[0083] Surprisingly, the lowest value of released sulfate is obtained at a BaCO concentration of 1%, which is not only sufficient to reduce the release of SO ions in solution, but also indicates that higher concentrations (e.g., 2%, 5%) are not necessary, but above all represent a particularly advantageous critical concentration.

[0084] Finally, experimental tests carried out by Applicant's engineers have shown that the particle size distribution of the metal salts / hydroxides used to combat the ion release phenomenon is also of utmost importance, with particle sizes above 100 microns in particular proving to reduce the effectiveness of the sequestration of the released ions.

[0085] Example 5: Braking performance test Brake pads prepared according to Example 1, i.e. with (test pads) or without (reference pads) 1% by weight of BaCO3, were subjected to the standard AK-Master braking test. The most important parts of the graphical results are shown in Figures 1 and 2.

[0086] As can be readily understood by those skilled in the art, FIGS. 1 and 2 show the friction coefficient μ (maximum (max), median (med), and minimum (min)) during an efficiency test consisting of three brake sections with 10 braking strokes in each section, as follows: First section: 50km / h~0km / h Second section: 100km / h~0km / h Third section: 120km / h~0km / h

[0087] From the figure, it can be seen that the target goal for standard performance is reached, i.e. 6 m / s 2 At a deceleration of 0.2 mm, the coefficient of friction μ remains higher than 0.3 for both materials (test and reference) and the measured pad wear is lower than 1.2 mm.

[0088] Consider now Figures 3 and 4, which show the same FADE section of the AK-Master test as Figures 1 and 2. Figures 3 and 4 show the variability of the coefficient of friction μ (maximum, median, and minimum values) with increasing temperature (top of these figures). The different temperatures result from different braking cycle runs. Again, the coefficient of friction remained within the target value of μ > 0.25.

[0089] As can be seen, the behavior of both tested brake pads (test and reference) is very similar and meets all standard market requirements in all sections, which shows that the presence of BaCO3 in the friction mixture is very effective in solving the problem of ion release, but does not affect braking performance.

[0090] Thus, all objectives of the present disclosure have been achieved.

[0091] [certain technical term] While certain braking devices, systems, and methods have been disclosed in the context of certain example embodiments, those skilled in the art will recognize that the scope of the disclosure extends beyond the specifically disclosed embodiments to the use of other alternative embodiments and / or embodiments, as well as certain modifications and equivalents thereof, such as brake shoes for brake drum-based braking systems. Use with any structure is clearly within the scope of the present invention. Various features and aspects of the disclosed embodiments may be combined with or substituted for one another to form various modes of assembly. The scope of the disclosure should not be limited by the specific disclosed embodiments described herein.

[0092] Conditional language such as "can," "could," "might," or "may," unless expressly stated otherwise or understood otherwise within the context as used, is generally intended to convey that a particular embodiment includes or does not include certain features, elements, and / or steps. Thus, such conditional language is generally not intended to imply that features, elements, and / or steps are in some way required for one or more embodiments.

[0093] Unless otherwise specified, the terms "approximately," "about," and "substantially," as used herein, refer to an amount close to the recited amount that still performs the desired function or achieves the desired result. For example, in some embodiments, as the context may indicate, the terms "approximately," "about," and "substantially" may refer to an amount within 10% or less of the recited amount. Similarly, the term "generally," as used herein, refers to a value, amount, or characteristic that primarily includes or tends toward a particular value, amount, or characteristic.

[0094] The present disclosure expressly contemplates that various features and aspects of the disclosed embodiments can be combined with or substituted for one another. Accordingly, the scope of the present disclosure should not be limited by the particular disclosed embodiments described above, but should instead be determined solely by a fair reading of the following claims along with their full scope of equivalents.

Claims

1. 1. An asbestos-free friction material composition comprising, as raw material ingredients, at least one filler, at least a fibrous material selected from the group consisting of inorganic fibers, organic fibers, metal fibers, and any combination thereof, at least one binder, at least one lubricant or friction modifier, and at least one abrasive, in combination with at least one water-soluble compound of a metal, which compound is capable of chemically reacting in the presence of water and / or moisture with ions optionally released / releasable by any of the raw material ingredients present in the friction material composition itself to form water-insoluble metal salts with such ions.

2. 2. The asbestos-free friction material composition of claim 1, wherein the water-soluble compound of the metal comprises a metal salt and / or a metal hydroxide that is readily soluble in water and, at the same time, is capable of forming water-insoluble salts with sulfate ions, sulfite ions, oxalate ions, and phosphate ions normally present in and / or, in some cases, released by the friction material composition.

3. 3. The asbestos-free friction material composition of claim 1, wherein the metal in the at least one water-soluble compound of the metal is selected from the group consisting of barium, calcium, aluminum, silver, and any combination thereof.

4. 4. The asbestos-free friction material composition according to claim 1, wherein the at least one water-soluble compound of a metal is a salt or hydroxide selected from the group consisting of barium carbonate, calcium hydroxide, aluminum triacetate, and silver acetate.

5. 5. The asbestos-free friction material composition according to claim 1, further comprising a specific amount of barium carbonate comprised between 0.5 and 10% by weight.

6. 6. The asbestos-free friction material composition according to any one of claims 1 to 5, characterized in that it comprises barium carbonate having a particle size distribution between 5 and 80 μm (microns).

7. 0.5 to 5% by weight of barium carbonate BaCO with a particle size distribution between 5 and 80 μm (microns) ３ 7. The asbestos-free friction material composition according to claim 5 or 6, comprising:

8. 8. The asbestos-free friction material composition of claim 1, wherein the at least one water-soluble compound of a metal is present in the friction material composition in an amount comprised between 0.5% and 10% by weight, inclusive of the extremes of that interval, calculated on the total weight of the friction material composition, and has a particle size distribution of less than 100 μm (microns).

9. Approximately 1% by weight of barium carbonate BaCO with a particle size between 5 and 80 microns ３ The asbestos-free friction material composition according to any one of claims 1 to 8, comprising:

10. 10. A brake element for a vehicle comprising a metal support and a layer or block of friction material carried by the support, wherein the block of friction material is made from the asbestos-free friction material composition of any one of claims 1 to 9, preferably molded onto a first surface of the support, and wherein the block of friction material is configured to capture / sequester and retain any ions, possibly released by one or more of the component materials of the friction material composition during use, in the form of water-insoluble metal salts within or on the friction material, without the ions being able to reach a friction partner of the block of friction material, such as a brake disc, and possibly causing chemical etching of the iron material therein.

11. 11. A braking element according to claim 10, characterized in that it is a brake pad or a brake shoe.

12. 10. A braking system comprising a braked member, the braking system comprising a brake disc or brake drum made of cast iron or steel, and at least one braking member constituted by a brake pad or brake shoe adapted to cooperate frictionally with the braked member, characterized in that the braking member has a friction layer intended to cooperate with the braked member, the friction layer being made of the friction material composition according to any one of claims 1 to 9.

Images