FIELD OF THE INVENTION

[0001] The invention relates to friction materials and more particularly to molded temperature resistant friction materials.

BACKGROUND OF THE INVENTION

[0002] Friction materials may be utilized in various applications such as clutches or driven devices to transfer torque between various components. Supercharger devices may include a clutch mechanism to engage and disengage the supercharger to provide various air charges to an internal combustion engine.

[0003] Supercharger clutches may include electromagnetically actuated dry clutches including a steel rotor surface that has a friction material disposed within a recessed pocket and engages with a steel armature surface when the supercharger needs to be engaged. The rotor may rotate at speeds up to 30,000 rpm which requires a friction material with sufficient hardness to provide the required long term wear resistance. The rotor and armature engagement at such speeds also requires a friction material with high thermal resistance.

[0004] There is therefore a need in the art for a friction material that is high thermal resistance and optimized hardness. There is also a need in the art for a friction material that has a long wear life and is resistant to noise vibration and harshness.

SUMMARY OF THE INVENTION

[0005] In one aspect, there is disclosed a temperature resistant molded friction material including: a base material including : a) a plurality of aramid fibers, the aramid fibers present in an amount of from 10 to 20% by weight of the base material; b) a silicate or titanate present in an amount of from 4 to 40% by weight of the base material; c) a metal present in an amount from

4 to 40% by weight of the base material; d) a mineral present in an amount from 4 to 20% by weight of the base material; and a resin impregnating the base material, the resin present in an amount of from 20 to 100 % by weight of the base material.

[0006] In another aspect, there is disclosed a temperature resistant molded friction material including: a base material including : a) recycled friction material present in an amount of from

40 to 90% by weight of the base material; b) carbon fibers present in an amount of from 5 to

30% by weight of the base material; c) graphite present in an amount from 1 to 10% by weight of the base material; d) molybdenum disulfide present in an amount from 1 to 10% by weight of the base material; and a resin impregnating the base material, the resin present in an amount of from

4 to 100 % by weight of the base material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] There is disclosed a molded friction material with specified hardness and thermal resistance formed of fibers, fillers, lubricants and abrasives bound together with a binder or resin material for high speed and high temperature dry clutch applications.

[0008] The molded friction material may include a base material including powders or short fibers having various sizes including nanoscale, milliscale and microscale sizes. The fibers and wires may include steel, copper, zinc, brass, lead, antimony, bismuth, molybdenum, barium sulfate, barium sulfide, molybdenum sulfide, molybdenum oxide, potassium titanate, tin sulfide, copper sulfide, lead sulfide, antimony sulfide, zirconium oxide, zirconium silicate, iron oxide, aluminum oxide, chromium oxide, boron nitride, boron carbide, calcium carbonate, mica, carbon, graphite, petroleum coke, polyacrylonitrile (PAN), cashew dust, rubber, polyphenylenes, aramid, glass, quartz, silicon carbide, rockwool, vermiculite, wollastonite, mullite and others.

[0009] The base material may include a plurality of aramid fibers. As used herein, the terminology“aramid” refers to aromatic polyamide fibers. The aramid fibers may be produced by a reaction between an amine group and a carboxylic acid halide group. For example, the aramid fibers may be a synthetic polyamide chain in which at least 85 parts by volume of amide linkages, i.e., an acyl group (R-C=O) bonded to a nitrogen atom (N), based on 100 parts by volume of the synthetic polyamide chain are attached directly to two aromatic rings.

[0010] The plurality of aramid fibers may be further defined as a plurality of para-aramid fibers having an average length of less than about 3 mm. That is, the plurality of aramid fibers may be short cut para-aramid fibers having a mean fiber length of about 1.4 mm and/or a bimodal mean fiber length of about 0.5 mm and about 1.4 mm. As used herein, the terminology

“about” is a quantity modifier, and refers to +/- 2% of the quantity being modified. The aramid fibers may be poly-(p-phenylene terephthalamdide) (PPTA) produced from the monomers p- phenylene diamine (PPD) and terephthaloyl dichloride (TDC) in a co-solvent with an ionic component such as calcium chloride to occupy hydrogen bonds of the amide groups, and an organic component N-methylpyrrolidone (NMP) to dissolve the aromatic polymer. After polymer production, the resulting aramid may be dissolved in water-free sulphuric acid and spun into filament yarn. The aramid fibers may be formed by shearing and chopping the filament yarn in water so that the aramid fibers are shortened and fibrillated. As compared to other fiber types, the plurality of aramid fibers may have a low degree of fibrillation. The plurality of aramid fibers may have a density of about 1.44 g/cm ³ . Suitable aramid fibers include Twaron ^® 1092 and Twaron ^® 1094, commercially available from Teijin Aramid GmbH of Arnhem, The Netherlands.

[0011] Also present in the base material is a silicate or titanate present in an amount of from

4 to 40% by weight of the base material. Exemplary materials include zirconium silicate and potassium titanate fibers or powders.

[0012] Also present in the base material is a mineral present in an amount from 4 to 20% by weight of the base material. Exemplary minerals include Lapinus,Wollastonite and Basalt fibers or powders.

[0013] Also present in the base material is a metal present in an amount from 4 to 40% by weight of the base material. Exemplary metals include steel and copper fibers or powders. The copper may be present in an amount of from 0-20 wt % and the steel may be present in an amount of from 0-30 wt %. All of the weight percents are based on the total weight of the base material.

[0014] Various filler materials may be included in the base material. The fillers if included include graphite (0-10 wt %), rubber (0-15 wt %), diatomaceous earth (0-13 wt %), sponge iron

(0-10 wt %), barium sulfate (0-13 wt %), molybdenum disulfide (0-5 wt %) and a metal oxide wherein the metal oxide is selected from aluminum oxide (0-20 wt%) and chromium oxide (0-4 wt%). All of the weight percent are based on the total weight of the base material.

[00151 In particular, the diatomaceous earth may be calcined diatomaceous earth having an average particle size of from about 10 microns to about 15 microns. As used herein, the terminology“calcined diatomaceous earth” refers to diatomaceous earth, i.e., sedimentary ore formed from freshwater planktonic species, that has been heat-treated, e.g., at temperatures at greater than about 800 °C, to round off shaip comers of individual diatomaceous earth particles.

Therefore, calcined diatomaceous earth may have reduced surface area as compared to natural, non-calcined diatomaceous earth, but increased hardness. As such, the presence of the calcined diatomaceous earth in the fibrous base material generally provides the friction material with excellent pressure-resistance.

[0016] The diatomaceous earth may have a pore size of from about 0.1 micron to about 1.0 micron, and may have a porosity of greater than 80 parts by volume based on 100 parts by volume of the diatomaceous earth. Further, the diatomaceous earth may have a mean particle size of from about 10 microns to 15 microns. Suitable diatomaceous earth includes Celite ^® 281, commercially available from World Minerals Inc. of Santa Barbara, California.

[0017] In another variation, the diatomaceous earth may be natural amorphous diatomaceous earth. That is, the natural amorphous diatomaceous earth may not be calcinated or dried. Natural amorphous diatomaceous earth provides the fibrous base material with excellent porosity. Suitable natural amorphous diatomaceous earth includes Diafil ^® 230, commercially available from World Minerals Inc. of Santa Barbara, California.

[0018] The binder can be in powder or liquid form, but powders of phenolic, modified phenolic (e.g. boron and phosphorus modified phenolic resin), silicone, rubber, polyimide, phthalonitrile, melamine, benzoxazine, epoxy or a mixture of several binders are preferred. The selection of the resin composition will depend on the hardness and thermal resistance requirements of the target clutch applications. In one aspect, the resin composition may have less than 5% weight loss at 500 C in a TGA test of the finished molded friction material. [0019] As set forth above, the fibrous base material is impregnated with the resin. The resin impregnates the fibrous base material to provide the friction material with mechanical shear strength, temperature-resistance, and friction stability. The resin also counterbalances the presence of the diatomaceous earth in the friction material and contributes to the enhanced friction stability of the friction material. Therefore, the resin may be a saturant and/or binder, and may have a viscosity of from about 90 cP to about 2000 cP at 25 °C. The resin may be any suitable resin selectable according to a desired application of the friction material. For example, the resin may be a phenol resin. In another variation, the resin may be a polyimide resin. Yet in other variations, the resin may be an epoxy- or oil-modified phenolic resin, silicone resin, mixtures of resins, multiple resin systems, and combinations thereof.

[0020] The fibrous base material may be impregnated with the resin at a resin pick-up of from about 20 parts by weight to about 100 parts by weight, e.g., about 35 parts by weight to about 50 parts by weight, based on 100 parts by weight of the fibrous base material. That is, the percent of resin pick-up by the fibrous base material, i.e., a weight percent of the resin based on the weight of the dry fibrous base material, may range from about 20% to about 100%. At resin amounts below about 20 parts by weight, the fibrous base material may not exhibit sufficient strength, and at resin amounts greater than about 100 parts by weight, the fibrous base material may be oversaturated so that the friction material exhibits poor porosity and lubricant absorption, resulting in glazing and noise, vibration, and harshness (NVH) sensitivity. Further, the aforementioned resin pick-up contributes to the excellent noise-resistance and pressure- resistance of the friction material by coating the fibrous base material. A suitable resin may include ASKOFEN 295 E 60, commercially available from Ashland-Stidchemie-Kemfest GmbH

(ASK Chemicals) of Hilden, Germany.

[0021] The manufacturing process steps of molded friction material include dry mixing, preform compaction, hot compaction, post baking and finishing steps. In the case of phenolic resins the pre-form compaction can be carried out at room temperature with 1 to 10 MPa pressure and in short press time. Hot compaction can be carried out at a temperature range from 150 C to 250

C with 10 to 100 MPa pressure for 1 to 30 minutes. During the hot compaction the pressure is relieved for several seconds after one, two and three minutes to allow gasses to escape. The post curing can be carried out at a temperature range from 200C to 300C under low pressure (less than 1 MPa) to preserve the dimensional stability for a time period ranging from 30 minutes to

30 hours. In the cases of high temperature resins such as polyimide and phthalonitrile the hot compaction and the post baking operations are conducted at 100-200C higher temperatures and longer times than those of phenolic resin. The final finishing operations may include cutting, drilling, flash removal, surface grinding/texturing and bonding.

[0022] The composition of the molded friction material may include several or all of the following additional materials listed in Table 1 and Table 2 outside of the aramid fibers, polyacrylonitrile carbon fibers and diatomaceous earth discussed above.

[0023] Table 1

[0024]

[0025] While some exemplary molded friction compositions are provided in Table 1 and

Table 2 the range of weight percentages of each component may be between 3 to 60% by weight based upon the total weight of the molded friction composition. The listed fiber materials such as aramid, polyacrylonitrile carbon fibers, basalt, rock wool micro fibers (e.g. Lapinus-RB-210), wollastonite, potassium titanate, steel, and copper are thermally stable and none of the fibers selected decomposes thermally at temperatures below 500 C in air.

[0026] The fillers that are optionally mixed into the resin(s) may be selected from: diatomaceous earth particles (e.g. Celite 281, Diafil 230), sponge iron, sulfates and sulfides (e.g. barium sulfate, antimony sulfate, molybdenum disulfide, tin sulfide, copper sulfide, antimony trisulfide, , silicate particles (e.g. sodium silicate, zirconium silicate, vermiculite, mica), metal oxide particles (e.g. AI ₂ O ₃ , CrO, CrO2, CrO3, Cr2O3, FeO, Fe3O4, Fe2O ₃ , ZrO2), carbide particles

(e.g. SiC, WC, B4C), nitride particles (e.g. BN, S ₃ N ₄ , WN), carbon particles (e.g. graphite, activated carbon, coke, carbon nanotubes etc.), rubber particles. The average size of the filler particles are in the range of 1 to 100 micrometers. Additionally, nano-sized particles may also be included. Micro-fiber filler materials may include an average length of from 20 to 300 micrometers.

[0027] Following the molding of the molded friction material, further final finishing operations include machining the inner and the outer diameters of the friction disk to the part specifications and drilling holes or cutting grooves as needed for the assembly or the application requirements.

[0028] The molded friction material is both thermally stable and has hardness in the range of 50 to 120 in Rockwell R scale measure with ½” diameter ball under 60 kg load to be used in the high speed rotation of a supercharger such as up to 30,000 ipm.

[0029] Recycled Friction Material [0030] In another aspect, the molded friction material may include recycled friction material from a previously cured friction material that includes a fibrous base material impregnated with a resin.

[0031] The recycled friction material may include a previously cured friction material that includes a fibrous base material impregnated with a resin.

[0032] The friction material may include mixing the recycled material with high temperature resins, reinforcing fibers and solid lubricants such as silicone resins, short carbon fibers, graphite and molybdenum disulfide particles to meet the strength, hardness, heat resistance and NVH resistance requirements of Super Charger Clutch applications.

[0033] The recycled material can be a dry or a wet friction material or a combination of both. The wet friction material can be E73 material manufactured by Eaton Corporation and as disclosed in Patents ( US8461064B2, US8563448B2, US8939269B2) which are incorporated herein by reference in their entirety for clutches used in Eaton's Torque Control Products.

[0034] In one aspect, the recycled friction material may be a cured friction material that includes aramid fibers, polyacrylonitrile-based carbon fibers and diatomaceous earth impregnated with a resin such as phenol resin, polyimide resin, epoxy- or oil-modified phenolic resin, silicone resin, mixtures of resins, multiple resin systems, and combinations thereof.

[0035] E73 material is made on a paper machine and is in sheet form that is about 6 feet wide. E73 friction material is an Eaton friction material made of high heat resistant ingredients and phenolic resin. A thin phenolic adhesive sheet is tacked on one side of the friction material to facilitate bonding over a steel core plate. The phenolic adhesive sheet is typically 0.04 mm to

0.12 mm thick and mostly 0.08 mm thick. The adhesive sheet is tacked on friction material at a 150F to 250F temperature range for less than 10 seconds under light pressure in 0.5 to 5 MPa range. The adhesive sheet is not fully cured under the tacking conditions. Either full rings of friction linings or segments of friction lining cut from the sheet of wet friction material are tacked with the adhesive sheet and bonded over steel core plates to make the friction plates. The final cure of adhesive and bonding to the steel core plate is accomplished at high pressures, greater than 5 MPa and high temperatures 400F-550F. Even though the material usage rate increases with segmenting still 30 to 40% of the friction material is discarded as scrap material in the original process. The scrap material can be recycled after chopping or grinding the scrap material into small pieces and then hot compacting them into a ring shape in a hot compression mold to produce a low cost molded dry friction material. The scrap friction materials have resin in them, however that resin has been almost fully cured and there is not enough bonding sites to create a strong cohesion within the molded friction material. However, the adhesive sheet tacked on the friction material is not fully cured and provides the necessary bonding sites to fuse the granulated friction material together during the hot molding process.

[0036] An improved material may be formed by mixing the scrap material with high temperature resins, reinforcing fibers and solid lubricants such as silicone resins, short carbon fibers, graphite and molybdenum disulfide particles to meet or exceed the strength, hardness, heat resistance and NVH resistance requirements of super charger clutch applications.

[0037] The resins may include phenolic, silicone, rubber, polyimide, phthalonitrile, polybenzoxazine, melamine or a mixture of several binders that can be in liquid or powder form.

The selection of the resin composition depends on the thermal resistance requirements of the target clutch applications. In one aspect, the selected resin composition may have less than 5% weight loss at 500 C in a TGA test. Silicone resins, ELASTOSIL®RT607 and

ELASTOSIL®RT60, made by Wacker may be utilized. The pick-up ratio of the resin to the recycled material can be in the range of 4 to 100% or in in the range of 10 to 40%. The reinforcements such as carbon fibers and solid lubricants, graphite and molybdenum disulfide, can be either mixed with the ground scrap material or mixed with the resin if the resin is in liquid form. A mixture of short and long carbon fibers may be utilized. More specifically, a new grade of milled carbon fibers in the range of 0.3 mm to 1 mm length and at least 94% crystalline carbon content may be used as the reinforcing fibers. Natural crystalline flake graphite grades such as F101 and F108 provided by Asbury may be utilized. Furthermore, commercial molybdenum disulfide particles such as ITAMoly 98 and McLube-MoS2 99 may be utilized. The exact proportions of the recycled material and the resins, fibers and particles are determined from the super charger clutch application requirements.

[0038] Table 3 lists the general range of ingredients and some examples of formulations in terms of weight percentages in the final product:

[0039] Table 3

[0041] The manufacturing process steps of molded friction material from recycled material include chopping, grinding, mixing, pre-form compaction, hot compaction, and finishing steps. The pre-form compaction can be carried out at room temperature with 1 to 10 MPa pressure and in short press time. Hot compaction can be carried out at a temperature range from 150 C to 250

C with 10 to 100 MPa pressure for 1 to 30 minutes. During the hot compaction the pressure may or may not be relieved for several seconds after one, two and three minutes to allow gasses to escape. The final finishing operations may include cutting, drilling, flash removal, surface grinding/texturing and bonding.

[0042] The molded friction material from recycled material is both thermally stable and has hardness in the range of 50 to 100 in Rockwell R scale measure with ½” diameter ball under 60 kg load to be used in the high speed rotation of a supercharger such as up to 30,000 rpm.