FRICTION DISK ASSEMBLY AND METHOD OF MAKING SAME

Abstract: A friction disk assembly ready for bonding to a core plate, and a method of making the same. An adhesive (30) for bonding the friction disk assembly (34) to the core plate (32) is applied to the rear surface of the annular friction ring (20). The pre-applied adhesive eliminates the expense and hazard of handling volatile adhesives during bonding of the friction ring to the core plate. The annular friction ring can be formed from at least two adjoining arcuate segments of a friction material. A porous backing (28) and the adhesive layer are applied to the rear surface of the friction material (22). Alternatively, the annular friction ring is a unitary structure. In another embodiment, the adjoining arcuate segments of a friction material are retained in an annular ring by the adhesive, without the porous backing. A method of bonding the friction disk assembly to a core plate is also disclosed.

Description: FRICTION DISK ASSEMBLY AND METHOD OF MAKING SAME Background The present invention is directed to a friction disk assembly and a method of making the same, and in particular, to a combination annular friction ring coated with an adhesive suitable for bonding the friction material to a core plate. Friction materials are used in a wide variety of different power transmission applications, such as for brake linings, brake pads, torque converter clutches in automatic transmissions, synchronizer rings for manual transmissions, and so-called "slip" clutches in newer automobiles (a variation of a torque converter clutch). The friction material is typically bonded to one or both sides of a metal core plate, that is then incorporated into the power transmission device. The annular friction rings were typically blanked out as one-piece rings from a continuous roll of friction material. U.S. Patent No. 4,260,047 (Nels) disclosed ninety degree arcuate segments stamped from a rectangular sheet of pre-grooved friction material in an effort to minimize waste. The segments were interconnected by opposing tabs and slots structured to form a complete annular friction ring, that was then bonded to an annular metal core plate. U.S. Patent No. 4,674,616 (Mannino) disclosed segmented core plates with interconnecting end portions to form the annular ring to which the segmented friction material was bonded. U.S. Patent No. 5,332,075 (Quigley et al.) recognizes that the segmented friction rings can be structurally fragile and can easily be damaged in the material handling process. Quigley proposes a segmented friction material locked together by a porous tape at the intersection of adjacent segments. The tape is placed on the rear of the segmented friction material so that it is sandwiched between the friction material and annular core plate. Preferably the tape used is of porous paper or fibrous cloth material that has an adhesive on one side. During the final bonding process, the porous tape allows the bonding adhesive to saturate through the tape and bond the metal plate to the entirety of the friction material, through the porous tape. U.S. Patent No. 5,361,480 (Gardener et al.) discloses a method of making torque converter clutches in which annular segments of friction material are stamped from a flat sheet into a holder ring, that is indexed to accept subsequent segments until a completed annular ring is constructed. The completed annular ring and holding ring are transported to a stripper station wherein the annular ring is stripped from the holder ring onto a heated metal clutch plate. The process of bonding friction material to core plates typically requires specialized equipment capable of handling adhesives. The adhesives typically contain volatile organic compounds, resulting in the expense associated with controlling any emissions and safely disposing of waste. Summary of the Invention The present invention is directed to a friction disk assembly ready for bonding to a core plate, and a method of making the same. In the various embodiments, an adhesive for bonding the friction disk assembly to the core plate is applied to the rear surface of the annular friction ring. The pre-applied adhesive overcomes the expense and hazard of handling volatile adhesives during bonding of the friction ring to the core plate. In a first embodiment, the annular friction ring is formed from at least two adjoining arcuate segments of a friction material. A porous backing and the adhesive layer are applied to the rear surface of the friction material. In a second embodiment, the annular friction ring is a unitary structure. In a third embodiment, two adjoining arcuate segments of a friction material are retained in an annular ring by the adhesive, without the porous backing. In one embodiment, the arcuate segments of friction material have interlocking ends. In another embodiment, the porous backing comprises at least two arcuate segments having interlocking ends. In an embodiment in which the porous backing is constructed from two or more arcuate segments, the arcuate segments of the backing are preferably joined at a location other than the location where the arcuate segments of the friction material are joined. Two, three or more arcuate segments of friction material may be used. In one embodiment, the arcuate segments of friction material comprise unequal lengths. The porous backing may be a paper, porous films of thermoplastic or thermoset materials, nonwoven webs of synthetic or natural fibers, scrims, or woven or knitted materials. The friction material may be conventional friction facing material or a microreplicated, patterned friction surface have a plurality of precisely shaped friction composites. Suitable adhesives include pressure sensitive adhesives, thermosetting or thermoplastic adhesives, radiation cured adhesives, adhesives activated by solvents, and blends thereof. The adhesive may include filaments. The porous backing can be laminated or impregnated with the adhesive. In another embodiment, the annular friction ring comprises a plurality of friction particles dispersed in a binder. The adhesive for bonding the friction disk assembly to the core plate is applied directly to the rear surface of the annular friction ring. In one embodiment, the front friction surface comprises a plurality of precisely shaped friction composites. The present invention is also directed to a method of manufacturing a friction disk assembly bondable directly to a core plate. At least two arcuate segments of a friction material are stamped. The arcuate segments of friction material are joined to form an annular ring. An annular ring of a porous backing with an adhesive is bonded to the rear surface of the annular friction ring. The present friction disk assembly is then bonded to a core plate using the adhesive. Depending on the nature of the adhesive, the adhesive can be activated by heat and pressure, solvents, RF energy, or a variety of other activating mechanisms. Brief Description of the Several Views of the Drawing Figure 1 is a side sectional view of a friction disk assembly in accordance with the present invention. Figure 2 is a perspective view of an assembled friction disk in accordance with the present invention. Figure 3 is a schematic illustration of a magazine containing a plurality of friction disk assemblies according to the present invention. Figure 4 is a top plane view of a blanking configuration for forming segments of friction material. Figure 5 is a side elevation view of one embodiment of a friction material for use in the present friction disk assembly constructed of precisely shaped friction composites. Detailed Description of the Invention Figure 1 illustrates a side sectional view of a friction disk assembly 20 in accordance with a first embodiment of the present invention. The friction disk assembly 20 includes a friction material 22 having a front friction surface 24 and a rear surface 26. The friction material 22 can be configured as a continuous, annular ring or segments. A porous backing 28 having an adhesive 30 is bonded to the rear surface 26 of the friction material 22. The adhesive 30 can be coated on the rear surface 26 of the friction material 22, coated on the porous backing 28, impregnated in the porous backing 28, or combinations thereof. The pre-applied adhesive 30 is subsequently used for bonding the friction disk assembly to core plate 32 to form a friction disk 34. The porous backing 28 may be paper, porous films of thermoplastic or thermoset materials, nonwoven webs of synthetic or natural fibers, scrims, or woven or knitted materials. Scrim refers to an loosely woven or nonwoven fabric with openings free of fibers or yarns. In an alternate embodiment, the porous backing 28 is omitted. Figure 2 is a perspective view of a friction disk 40 in accordance with the present invention. Annular core plate 42 typically includes spline teeth 44 along an inner surface 46. Friction disk assemblies 48 are bonded to opposite sides of the core plate 42. In the embodiment illustrated in Figure 2, the friction disk assemblies 48 are formed from a plurality of adjoining arcuate segments 50 of a friction material bonded to an annular ring of a porous backing 52 that includes an adhesive 54. The arcuate segments 50 are joined by tab and slot configured edges 56. The arcuate segments 50 may include oil channels 51. Optionally, the porous backing can be formed from arcuate segments joined at locations 58, preferably off-set from the tab and slot configured edges 56. Adhesive 54 bonds the friction disk assembly 48 to the annular core plate 42. In an alternate embodiment, the adhesive 54 may have sufficient tensile strength to retain the arcuate segments 50 in an annular ring without the porous backing 52. Fillers, including fibrous materials may be added to increase the structural integrity of the adhesive 54, and hence, make the friction disk assembly 48 suitable for machine handling. Bonding of the friction disk assembly 48 to the annular core plate 42 is typically accomplished by activating the adhesive 54 using a variety of techniques, such as with heat and/or pressure. Alternatively, the adhesive 54 can be activated by solvents, radiation energy, (including visible light, UN, radio waves, microwaves), heat and/or pressure, electron beam energy, moisture, the absence of air, or combinations thereof. Figure 3 is a schematic illustration of a magazine 60 containing a plurality of friction disk assemblies 61 in accordance with the present invention. The magazine 60 includes a housing 62 for retaining the friction disk assemblies 61 and an ejection slot 64. The friction disk assemblies 61 have sufficient structural integrity to permit high speed machine handling for bonding to core plates (see Figures 1 and 2). Additionally, the pre-applied adhesive eliminates the need for adhesive handling equipment. In some embodiments, the adhesive is free of volatile organic compounds at the point in the process where the friction disk assemblies 61 are ready to be bonded to the core plates. Figure 4 is a top plan view of a blanking configuration 70 to optimize the yield of arcuate segments 72 from the friction material 74. The segments 72 are of progressively shorter lengths so as to form a pie-shaped wedge 76. By arranging the wedges 76 in an alternating arrangement, the amount of wasted friction material 74 is dramatically reduced. The ends of the arcuate segments 72 may be straight 78 or shaped to form a tab and slot engagement 79 with an adjoining segment. For example, segments 72 of unequal lengths can be cut to cover 92 degrees, 82 degrees, 72 degrees, 62 degrees and 52 degrees (360 degrees total), or any other configuration that corresponds to the surface area of the friction material 74. In general, the desired attributes of a friction material include toughness, strength, heat resistance, good frictional properties, and long life. Friction materials for transmissions should have a generally level torque curve, display no bond failure under standard usage conditions, and have retention of torque curve levelness and torque capacity. In addition, as smooth operation of the clutch is enhanced by friction modifiers in the transmission fluid, the friction material should hold or retain an appropriate amount of fluid at the engaging surface. U.S. Pat. No. 5,083,650 (Seitz et al.) discloses a friction member having a roughened surface suitable for use as a friction facing member in a transmission. The friction member of Seitz et al. involves a heat-resistant paper supporting granular carbon friction particles resin-bonded via underlying and overlying thermoset polymeric binder containing carbon filler particles. An undulated (roughened) contour is formed on the surface of the friction member of Seitz et al. Suitable commercially available friction materials are available from Minnesota Mining and Manufacturing Company of St. Paul, MN, under the product designations FMA15 and FMM10. Figure 5 illustrates an alternate friction material having a patterned friction surface with a plurality of precisely shaped friction composites, such as disclosed in PCT Publication No. WO 97/38236 entitled "Patterned Surface Friction Materials, Clutch Plate Members and Methods of Making and Using Same". Alternate friction material 80 comprises a backing 82 with a front surface 84 and a back surface 86. The backing 82 may optionally include a plurality of reinforcing fibers 87, such as aramide polymer staple fibers. Bonded to the front surface 84 of the backing 82 is a friction coating 88. Friction coating 88 has an inner surface 90 and a patterned friction surface 92 defined by a plurality of precisely shaped friction composites 94. The friction composites 94 comprise a binder 96 and a plurality of friction particles 98. The binder 96 attaches the composites 94 to the front surface 84 of the backing 82. As seen in Figure 5, a portion of the binder 96 and friction particles 98 dispersed therein may seep into the backing 82. Adhesive 85 for bonding the friction disk assembly 91 to a core plate is applied to the back surface 86 in accordance with the present invention. In an alternate embodiment, the friction composites 94 may be formed directly onto the adhesive layer 85, as will be discussed below. In the illustrated embodiment, the precisely shaped friction composites 94 are pyramidal in shape. Alternatively, the friction composites 94 can be any shape, but preferably a geometric shape in cross-section or three-dimensions being such as a rectangle, cone, truncated pyramid, semicircle, circle, triangle, square, hexagon, pyramid, octagon, gum drops, conical and the like. The preferred shapes are triangular-based and quadrilateral-based pyramids. It is also preferred that all of the friction composites decrease in cross sectional area proceeding in the direction away from the backing up towards the distal end, whether it be pointed, flat topped or rounded. In general there are at least 5 friction composites 94 per square centimeter, in some instances, at least 500 friction composites per square centimeter. In general, a range of about 120 to about 1150 composites per square centimeter is suitable; although higher or lower values may be optimal depending on the circumstances. For friction material applications, the height H of the friction composites generally is in the range of about 88 micrometers to about 534 micrometers. The expression "precisely shaped friction composites", as used herein, refers to friction composites having a shape that has been formed by curing the flowable mixture of friction particles and curable binder while the mixture is both being borne on a backing and filling a cavity on the surface of a production tool (described herein). Such a precisely shaped friction composite would thus have precisely the same shape as that of the cavity. The plurality of such composites provide three-dimensional shapes that project outward from the surface of the backing and land portion in a non-random pattern, namely the inverse of the pattern of the production tool. Each composite is defined by a boundary, the base portion of the boundary generally being the interface with the front surface of the backing to which the precisely shaped composite is adhered. The remaining portion of the boundary is defined by the cavity on the surface of the production tool in which the composite was cured. Adhesive Suitable adhesives for bonding the friction disk assemblies to the core plates include pressure sensitive adhesives, thermosetting or thermoplastic adhesives, radiation cured adhesives, adhesives activated by solvents, and blends thereof. Specific examples of suitable adhesives are disclosed in U.S. Patent Nos. 5,436,063 (Follett et al.); 5,580,647 (Larson et al.); 5,582,672 (Follett et al.); 5,595,578 (Stubbs et al.); 5,611,825 (Engen et al.); 5,681,612 (Benedict et al.); and 5,709,948 (Perez et al.). One particularly preferred adhesive for use with the friction disk assembly of the present invention is a latex-phenolic blended resin which is used in a film form. A ratio of about 30 to about 70 parts by dry weight latex resin to about 70 to about 30 parts by dry weight resole phenolic resin, both resins being less than 100% solids, is thoroughly mixed and then coated, for example via a knife coater, to form a film. The coating can be applied to a release liner or can be applied so that it saturates a scrim material. The coating is then dried so that it is approximately 100% solids and the resulting film is a handleable structure. The latex-phenolic film can then be bonded to the segmented friction material via heat and/or pressure. The heat and/or pressure should be sufficient to bond the adhesive and the scrim to the friction material, but should not proceed as far as the final cured stage. Once the friction material having the adhesive thereon is brought into contact with the core plate, the adhesive is preferably cured to it final state by the application of high heat and high pressure. Another particularly preferred adhesive for use with the friction disk assembly of the present invention is a blend of a thermoplastic resin and a thermosetting resin. Preferably, this hybrid adhesive comprises a polyester resin and an epoxy resin in a ratio of about 10 to about 40 parts by weight polyester to about 90 to about 60 parts epoxy. The epoxy may be a mixture of various epoxy-functional resins. Generally, a curative agent is added to aid the curing of the epoxy. The two resins, both 100% solids, are melt blended and then coated to form a film. The coating can be applied onto a release liner or onto a scrim. The adhesive can thoroughly or partially saturate the scrim, or remain on top of the scrim without actually soaking into the scrim. The coating is then solidified so that the resulting film is a handleable structure. Similar to the latex-phenolic, the hybrid adhesive can be bonded to the segmented friction material via gentle heat and/or pressure. Then, the friction material is bonded to the core plate under high heat and high pressure. In some instances it may be preferred to include an additional curing component in the hybrid adhesive which may improve processing. For example, a multi-functional acrylate resin, when added to an epoxy, can reduce the amount of flow of the adhesive during the thermal cure. The acrylate could be cured with electron beam radiation or UN light and the aid of a photoinitiator. In one embodiment, the adhesive is one that is capable of irreversibly forming a cured oligomeric/polymeric material and is often used interchangeably with the term "thermosetting" adhesive. The term "thermosetting" adhesive is used herein to refer to reactive systems that irreversibly cure upon the application of heat and/or other sources of energy, such as E-beam, ultraviolet, visible, etc., or with time upon the addition of a chemical catalyst, moisture, or the like. The term "reactive" means that the components of the adhesive react with each other (or self react) either by polymerizing, crosslinking, or both, using any of the mechanisms listed above. These components are often referred to as resins. As used herein, the term "resin" refers to polydisperse systems containing monomers, oligomers, polymers, or combinations thereof. Thus, materials suitable for forming the adhesive comprise reactive components, i.e., materials capable of being crosslinked and/or polymerized, by a wide variety of mechanisms. Examples include, but are not limited to amino resins such as alkylated urea- formaldehyde resins, melamine-formaldehyde resins, and alkylated benzoguanamine- formaldehyde resins; acrylate resins (including acrylates and methacrylates); alkyd resins such as urethane alkyd resins; polyester resins; aminoplast resins; urethane resins; phenol formaldehyde resins (i.e., phenolic resins) such as resole and novolac resins; epoxy resins such as bisphenol epoxy resins; isocyanates; isocyanurates; silicone resins; cashew nut shell resins; polyimide resins; ester resins; bismaleimide resins; and the like. Such reactive adhesive components are capable of being cured by a variety of mechanisms (e.g., condensation or addition polymerization) using, for example, thermal energy, radiation energy, etc., or a combination of mechanisms. Adhesives that can be cured with rapidly acting forms of radiation energy (e.g., requiring application for less than five minutes and preferably for less than five seconds) are particularly preferred. Useful forms of radiation energy include ultraviolet/visible light, nuclear radiation, electron beam, infrared, and microwave radiation. Depending on the particular curing mechanism, the adhesive can further include a catalyst, initiator, or curing agent to help initiate and/or accelerate the polymerization and/or crosslinking process. Another type of initiator system particularly desired is a thermal initiator, i.e., one which requires heat to initiate the polymerization. A thermal initiator is also preferred because of its ability to penetrate heavily pigmented coatings, its speed and efficient use of applied energy, and its ease of control. A thermal initiator can be used alone or in combination with another initiator, such as a UN photoinitiator which can be used in an exothermic system compatible with the thermal initiator. In this type of system, UN radiation can be used to initiate the reaction, which then provides the heat needed to initiate the thermal initiator. With the addition of the thermal initiator to the system, any requirement of post-curing of the material may be eliminated. Examples of commercially available thermal initiators include VAZO 52 and NAZO 64 FREE RADICAL SOURCES both from DuPont, Wilmington, DE, and TRIGOΝOX 21-C50 (tert-butylperoxy-2- ethylhexanoate) from Akzo Νobel, Chicago, IL. Of course, the initiator selected for the application depends on the chemistry of the system and on the amount of heat available in the reaction. Adhesive components capable of being cured by thermal energy and/or time with the addition of catalysts include, for example, phenolic resins such as resole and novolac resins; epoxy resins such as bisphenol A epoxy resins; and amino resins such as alkylated urea-formaldehyde resins, melamine-formaldehyde resins, and alkylated benzoguanamine- formaldehyde resins. The adhesive containing reactive components such as these can include free radical thermal initiators, acid catalysts, etc., depending on the resin system. Examples of thermal free radical initiators include peroxides such as benzoyl peroxide, azo compounds, benzophenones, and quinones. Typically, such reactive seal coat adhesive components need temperatures greater than room temperature (i.e., 25-30°C) to cure, although room-temperature curable systems are known. Resole phenolic resins have a molar ratio of formaldehyde to phenol, based upon weight, of greater than or equal to about 1:1, typically about 1.5:1.0 to about 3.0:1.0. Novolac resins have a molar ratio of formaldehyde to phenol, based upon weight, of less than about 1:1. Examples of commercially available phenolic resins include those known by the designations DUREZ and VARCUM from Occidental Chemicals Corp., Dallas, TX; RESINOX from Monsanto, St. Louis, MO; and AEROFENE and AEROTAP from Ashland Chemical Co., Columbus, OH. Epoxy resins are polymerized by oxirane ring opening. These resins can vary greatly in the nature of their backbones and substituent groups. For example, the backbone may be of any type normally associated with epoxy resins, and the substituent groups may be any group free of an active hydrogen atom that is reactive with an oxirane ring at room temperature. Representative examples of acceptable substituents include halogens, ester groups, ether groups, sulfonate groups, siloxane groups, nitro groups, and phosphate groups. One of the most commonly available epoxy resins is the reaction product of diphenylol propane (i.e., bisphenol A) and epichlorhydrin to form 2,2-bis[4-(2,3-epoxypropoxy) phenyljpropane (a diglycidyl ether of bisphenol A). Such materials are commercially available under the trade designations EPON (e.g., EPON 828, 1004, and 1001F) from Shell Chemical Co., Houston, TX, and DER (e.g., DER 331, 332, and 334) from Dow Chemical Co., Midland, MI. Other suitable epoxy resins include glycidyl ethers of phenol formaldehyde novolac resins available under the trade designation DEN (e.g., DEN 431 and 428) from Dow Chemical Co. Amino resins are the reaction product of formaldehyde and an amine. The amine is typically urea or melamine. The most common amino resins are the alkylated urea- formaldehyde resins and melamine-formaldehyde resins, although alkylated benzoguanamine-formaldehyde resins are also known. Melamine-formaldehyde resins are typically used where outdoor durability and chemical resistance are desired. Typically, however, amino resins are not used by themselves because they tend to be brittle. Thus, they are often combined with other resin systems. For example, they can be combined with alkyds, epoxies, acrylics, or other resins that contain functional groups that will react with the amino resin, to take advantage of the good properties of both resin systems. In some embodiments, the adhesive may include at least one resin having at least one pendant acrylate group. A suitable resin having at least one pendant acrylate group may be selected from the group of a monofunctional acrylate monomer, a multifunctional acrylate monomer, a urethane acrylate, an epoxy acrylate, an isobornyl acrylate, a polyester acrylate, an acrylated acrylic, a silicone acrylate, a polyether acrylate and mixtures thereof. As used herein, the terms "acrylate" and "acrylate functional" compound includes both acrylates and methacrylates, whether they be monomers, oligomers, or polymers. A urethane acrylate is a diacrylate ester of hydroxy terminated isocyante extended polyester or polyether. It can be aliphatic or aromatic. Examples of commercially available urethane acrylates include those known by the trade designations PHOTOMER (e.g., PHOTOMER 6010) from Henkel Corp., Hoboken, NJ; EBECRYL 220 (hexafunctional aromatic urethane acrylate of molecular weight 1000), EBECRYL 284 (aliphatic urethane diacrylate of 1200 molecular weight diluted with 1,6-hexanediol diacrylate), EBECRYL 4827 (aromatic urethane diacrylate of 1600 molecular weight), EBECRYL 4830 (aliphatic urethane diacrylate of 1200 molecular weight diluted with tetraethylene glycol diacrylate), EBECRYL 6602 (trifunctional aromatic urethane acrylate of 1300 molecular weight diluted with trimethylolpropane ethoxy triacrylate), and EBECRYL 8402 (aliphatic urethane diacrylate of 1000 molecular weight), all available from UCB Chemical, Smyrna, GA; SARTOMER (e.g., SARTOMER 9635, 9645, 9655, 963-B80, 966-A80, etc.) from Sartomer Co., West Chester, PA; and UVITHANE (e.g., UVITHANE 782) from Morton International, Chicago, _L. Other useful resins having at least one pendant acrylate group include those available under the trade designation SARTOMER CN 966-J75 (a difunctional aliphatic urethane acrylate oligomer blended with 25% isobornyl acrylate) from Sartomer Co., West Chester, PA; and EBECRYL 350 (a silicone ester acrylate oligomer) from UCB Chemical; aromatic acid methacrylate half ester blended with either difunctional (SR506) or trifunctional (SR454) monomer, available under the tradenames SB570A20 and SB510G35, respectively; and aromatic acid acrylate half ester blended with either monofύnctional (SR334) or trifunctional (SR454) monomers, available under the trade designations SB520E35 and SB520M35, respectively, all commercially available from Sartomer Co. Porous Backing The selection of the particular porous backing employed will depend upon the desired application of the friction material. Typically, the backing should be heat resistant and strong. The heat resistance and strength properties are necessary to ensure that the friction disk assembly will withstand the forces and heat generated during use. In some applications, for example when the inventive friction disk assembly is employed in synchronizer rings, the porous backing should be flexible to conform to the blocker ring (i.e., the synchronizer). In other applications, the porous backing should be substantially incompressible (after bonding) since the brake pad should be essentially rigid and nonconforming. It is preferred that the thickness of the porous backing be very constant or very uniform along its width and length. The thickness should not vary by more than about 20%, preferably not more than about 10% at any point. The porous backing thickness can range from about 0.05 mm to about 10 mm, typically from about 0.05 mm to about 1.0 mm. A backing thickness of about 0.13 mm is suitable for most applications. The thickness values for the backing of the invention can be measured in accordance with TAPPI T411 OM Test Method. The thickness selected for the porous backing is influenced by several considerations, such as sufficient thickness for the resilience desired; as thin as possible for reasons of economy; and as thick as needed for the particular clutch environment requirements. The porous backing typically and preferably comprises a fibrous material or is made from a fibrous material. The fibers of the fibrous material can be organic (either synthetic or natural) or inorganic fibers, or combination thereof. Examples of synthetic fibers include those made from polycarbonate, polyvinylchloride, polyetherimide, polyethylene, polyurethane, polyester, polysulfone, polystyrene, acrylonitrile-butadiene-styrene block copolymer, polypropylene, acetal polymers, nylon, aramid, polyimide copolymers and physical blends thereof. Examples of natural organic fibers include cotton, wool, silk, cellulose, rayon, hemp, kapok, flax, sisal, jute, manila, and combinations thereof. Examples of suitable inorganic fibers include metallic fibers, alumina fibers, glass fibers, and fibers made from ceramic materials such as those commercially available from 3M under the trade designation "NEXTEL", which comprise about 60-70% alumina, 20-30% silica, and 1-20% boria. Nonwoven mats made using these fibers are available under the trade designations "NEXTEL 312" and "NEXTEL 440". Carbon fiber webs also may be used. Where heat is an issue, one material useful as a backing in the friction disk assembly of the present invention is a nonwoven paper comprising aramid polymer staple fibers bonded with an acrylic latex to provide a uniform density backing. It has been found that great care must be taken in order to obtain a uniform density, uniform thickness aramid staple fiber nonwoven in order to provide a suitable friction material backing. The aramid staple fibers for this purpose preferably have a length of about 0.5 cm to about 2 cm, and more preferably about 1.0 to about 1.5 cm. At lengths longer than about 2 cm (such as 5 cm or greater), the fibers tend to form dense areas which make the backing unacceptably dense. Fibers shorter than about 0.5 cm (such as 0.05 cm or less) do not easily form backings with adequate handling strength. The backings also preferably have a weight of about 5 g/m 2 to about 50 g/m 2 (more preferably about 10 g/m 2 to about 25 g/m 2 ) to provide sufficient structural support for the friction coating. Aramid polymers suitable for use in producing the aramid staple fibers are commercially available from I.E. DuPont de Nemours Company, Wilmington, DE, under the trade designations "KEVLAR", "KEVLAR 29", "KEVLAR 49", and "NOMEX". The term "aramid polymer" as used herein means a synthetic polymer resin generally designated in the art as an aromatic polyamide. Such "aramid polymers" are disclosed in U.S. Patent Nos. 3,652,510 (Blomberg); and 3,699,085 (Johnson), and are thought to be of a polymer of high molecular weight, e.g., having an inherent viscosity of at least about 0.7. Illustrative examples of polyamides include poly (p-phenylene terephthalamide), chloro- substituted poly (p-phenylene terephthalamide), and copolymers thereof. Although the aramid polymer or aromatic polycarbonamide may consist primarily of carbonamide links (-CONH-) and aromatic ring nuclei, conforming to the formula above, the polymer may contain up to about 20 mole percent and preferably up to about 5 mole percent of nonconforming comonomer units which provide units in the polycarbonamide chain different than those listed above, such as aromatic carbonamide units whose chain extending bonds are coaxial or parallel and oppositely directed, e.g., meta-phenylene units, non-aromatic and non-amide groups. It is important that the aramid polymers utilized to obtain the unique advantages of the invention are in the staple form of aramid fibers. The length of the staple fiber, as previously mentioned, is about 0.5 cm to about 2 cm. The aramid fiber nonwoven papers previously described, are made by conventional paper making techniques, and are commercially available from Veratec Corp., a division of International Paper of Tuxedo, NY, under the trade designations "KEVLAR" Mat Series "8000050", "8000051", "8000052", "8000054", "8000065" and "8000068". These papers include about 8 weight percent to about 18 weight percent acrylic latex used to consolidate the fibers into an integral web. The balance of the weight is made of the aramid fibers. Example 1 - Friction Disk Assembly A 0.4 ounces/square yard KEVLAR paper available from Veratec Corp. was saturated with a 60/40/50 (wet basis) mixture of 208.3 grams HYCAR 1578X1 latex, 13.3 grams BOSTEX 422 zinc oxide dispersion, 2.9 grams BOSTEX 410 sulfur dispersion, 4.0 grams BOSTEX 497-B butyl zimate dispersion (all available from Akron Dispersion of Akron, OH)/water-based resole phenolic resin/petroleum coke available from Asbury under the designation 4023, and allowed to dry. The impregnated KEVLAR pieces were tacked to a friction material at about a 45 degree offset using a hot iron for a few seconds. The friction material is available from 3M of St. Paul, MN, under the product designation FMA 15. The resulting friction disk assembly was bonded to a steel core plate in a press heated to about 205°C (400°F) for about two minutes under a ram pressure of about five tons. Shims were used to achieve a uniform final caliper. Example 2 - Segmented Friction Disk Assembly Adhesive and nonwoven reinforced adhesive films were prepared from a mixture made of 21 parts DYNAPOL S1402 (Creanova, Inc; Somerset, NJ), 40 parts EPON 100 IF (Shell Chemical, Houston, TX), 30 parts EPON 828 (Shell Chemical, Houston, TX), 9 parts TMPTA-N (UCB Chemicals; Smyna, GA), 1 part IRGACURE 651 (Ciba Specialty Chemicals, Hawthorne, NY), and 1 part 2-ethylimidazole (Aldrich Chemicals, Milwaukee, WI). To prepare the adhesive and reinforced adhesive films, the listed mixture was heated to 130°C for knife coating on a common carrier film. During the coating step, the coater knife was heated to 120°C, the coater bed was heated to 65 °C and the knife gap was set at 6 mil (distance between the top of the carrier film and the bottom of the knife). A nylon nonwoven reinforcement, CEREX 210512 (commercially available from Cerex Advanced Fabrics L.P., Pensacola, FL), was placed between the knife and the carrier film. The heated adhesive mixture was placed on top of the CEREX reinforcement and the carrier film was pulled under the knife to coat the adhesive. Enough adhesive mixture was applied so that the adhesive mixture continued to be coated on the carrier film after the end of the CEREX reinforcement had passed under the knife. After coating, the adhesive and reinforced adhesive films on the carrier film were irradiated by passing under a 600 watt D bulb at 50 feet/minute to partially cure the adhesive mixture. Both the adhesive and reinforced adhesive films were cut into quarter circle segments having ball and socket joints at the ends of each segment using a quarter circle steel rule die. The adhesive segments were then joined to similarly shaped friction facing segments. The friction facing segments were made from the following components. The listed components were combined, with mixing, into the slurry in the order listed and further mixed until all the components were well dispersed. The dispersed slurry was coated onto a textured production tooling. The tooling used to generate the friction facing texture was polypropylene sheet having a microreplicated surface of flat top pyramids with dimensions of 14 mils height, 12.5 x 12.5 mils tops, 6 mils spacing, and 10° draft angle. The microreplicated tooling was placed microreplicated side up under a coater knife and the gap between the tooling and knife was set at 3 mils. A carrier film was placed under another coater knife and the gap was set at 5 mils. The mixed slurry was applied over the tooling and carrier film at their respective coaters and a nonwoven backing of 0.5 oz/yd 2 KEVLAR paper (obtained commercially from Veratec Division of International Paper) was introduced between the two coated slurry layers. The two layers of the slurry composition and the nonwoven backing were forced together by a pinch roll and UV energy was applied to cure the slurry layers. The coating line speed was 30 feet/minute and the UN energy source was two 600 watt D bulbs. After cure the slurry, the tooling and carrier films were removed from the friction facing which was then cut into quarter circle segments using a quarter circle steel rule die. The friction facing segments were then combined with the adhesive film segments. Two friction facing segments were placed textured side down in a simply circular assembly form that held the segments in the desired positions and the adhesive film or reinforced adhesive film segments were placed adhesive side down over the two friction facing segments, so that about one half of the adhesive segment was on each friction facing segment. The adhesive segments were tacked to the friction facing segments by pressing them together with a cool iron (surface temperature about 40 to 60°C, enough to soften the adhesive and allow the segments to adhere, but not hot enough to further cure the adhesive film). Another friction facing segment was placed in the assembly form and another adhesive segment was pressed on top of it. A final friction facing segment and adhesive segment were added to complete the circular assembly. The assembly was placed in a freezer to facilitate carrier film removal from the adhesive film. After the carrier film was removed from the adhesive film, the assembly was placed adhesive side down on a cleaned steel core plate. The assembly was tacked in place with a cool iron. A second assembly was placed on the other side of the cleaned core plate and tacked in place with a cool iron. The thickness of the tacked assembly was measured with a micrometer and shims were selected to give about 1 to 2 mils (0.02 to 0.05 mm) compression during bonding. The tacked assembly was placed in a press with the selected shims and pressed at 205°C and 5000 lbs. ( 8900 Newtons ) total load for 2 minutes.

Claims: Claims 1. A friction disk assembly ready for bonding to a core plate, comprising: an annular friction ring formed of at least two adjoining arcuate segments of a friction material, the friction material having a front friction surface and a rear surface; an annular ring of a porous backing located opposite the rear surface; and an adhesive for bonding the friction disk assembly to the core plate applied to the rear surface of the annular friction ring. 2. The friction disk assembly of claim 1 wherein the at least two arcuate segments of friction material comprise interlocking ends. 3. The friction disk assembly of claim 1 wherein the porous backing comprises at least two arcuate segments joined at a location other than a location where the arcuate segments of friction material are adjoined. 4. The friction disk assembly of claim 1 wherein the at least two arcuate segments of friction material comprise unequal lengths. 5. The friction disk assembly of claim 1 wherein the porous backing is impregnated with the adhesive. 6. The friction disk assembly of claim 1 wherein the front friction surface comprises a plurality of precisely shaped friction composites. 7. The friction disk assembly of claim 1 wherein the adhesive retains the porous backing to the rear surface. 8. A friction disk assembly ready for bonding to a core plate, comprising: an annular friction ring formed of at least two adjoining arcuate segments of a friction material, the friction material having a front friction surface and a rear surface; and an adhesive for bonding the friction disk assembly to the core plate and for retaining the adjoining segments of friction material in an annular friction ring applied to the rear surface thereof. 9. The friction disk assembly of claim 8 wherein the adhesive comprises reinforcing fibers . 10. The friction disk assembly of claim 8 wherein the front friction surface comprises a plurality of precisely shaped friction composites. 11. A method for manufacturing a friction disk assembly ready for bonding to a core plate, comprising the steps of: stamping at least two arcuate segments from a friction material, the friction material having a front friction surface and a rear surface; joining the arcuate segments of friction material to form an annular friction ring; and retaining an annular ring of a porous backing to the rear surface of the annular friction ring with an adhesive for bonding the friction disk assembly to the core plate.

Inventors: DAHLKE GREGG D, IONTA RICHARD, MCKEAGUE KARL T, SEITZ DAVID S, DAHLKE, GREGG, D., IONTA, RICHARD, MCKEAGUE, KARL, T., SEITZ, DAVID, S.
Applicants: 3M INNOVATIVE PROPERTIES CO, 3M INNOVATIVE PROPERTIES COMPANY
Application year: 1999
Main classification: F16D13
IPC codes: F16D13, F16D23, F16D69, F16H45