COMPOSITE ABRASIVE FILAMENTS, METHODS OF MAKING SAME, ARTICLES INCORPORATING SAME

Abstract: A composite abrasive filament, including at least one preformed core at least partially coated with a hardened, abrasive-filled thermoplastic elastomer, exhibits increased abrading life over previously known abrasive filaments. Previously known abrasive-filled nylon filaments have limited stiffness and lose their stiffness as temperature approaches 70 DEG C. The composite abrasive filaments of the present invention are more efficient and more resistant to flex fatigue failure than abrasive-filled nylon filaments. Also disclosed are methods of making such filaments and using such filaments in article form to abrade a variety of workpieces.

Description: COMPOSITE ABRASIVE FILAMENTS, METHODS OF MAKING SAME, ARTICLES INCORPORATING SAME 5 TECHNICAL FIELD The present invention relates to composite abrasive filaments comprising preformed cores coated with an abrasive-filled thermoplastic elastomer. BACKGROUND ART 10 Nylon abrasive filaments were developed in the late 1950's as a man made alternative to natural abrasive filaments. At about that time an extrusion process was developed for dispersing abrasive particles uniformly in a nylon matrix in the form of a filament (U.S. Pat. Nos. 3,522,342 and 3,947,169). A review of nylon abrasive filaments is presented by Watts, J.H. , "Abrasive 15 Monofilaments-Critical Factors that Affect Brush Tool Performance", Society of Manufacturing Engineers Technical Paper, 1988, a written version of a presentation by the author at the WESTEC Conference, held March 21-24, 1988. As explained by Watts, as filaments of this type wear, new abrasive particles are exposed. An abrasive filament brush tool made using a plurality 20 of these filaments is thus regenerated during use. Some of the advantages of nylon abrasive filaments are their safety, cleanliness, cutting speed, low cost, superior radius and finish control, adaptability, and ease in design. A key property of nylon and other thermoplastic materials is its "memory". In a brush filament this is referred to in the art as "bend 25 recovery" , or the tendency for a deflected filament to return to its original deployment. The bend recovery for nylon is generally over 90%, i.e., the filament returns to about 90% of its original deployment after being deflected. Over time in operation, such as in a brush tool, most abrasive-filled polymeric filaments will take a set shape, and unless the filaments of the brush 30 tool recover, the brush tool becomes soft and loses its effectiveness. Bend recovery is determined by filament diameter, relaxation time, strain, deflection time, and environmental conditions. Among synthetic filaments made to date, nylon offers the best bend recovery from strain held for an extended period of time. While adequate for many purposes, the inventors herein have found that the various nylons have property limitations which make their use less than optimal in abrasive filaments. Nylon abrasive filaments have limited stiffness and may lose their stiffness as filament temperature approaches 70 °C, and thus may not be suitable for removing heavy scale or burrs when elevated filament temperatures are developed. Temperature resistance is critical in maintaining filament stiffness. Elevated temperatures generally affect all nylon polymers in a similar way: stiffness, as measured by the bending (tangent) modulus, decreases as temperature increases. Heat generation is normally not a problem in long filament deburring where brush tool speeds are low. However, in short trim power brushes, tool pressure on the part and/or high speed in a dry environment can generate high temperatures at the filament tips. Another limitation of nylon abrasive filaments is that moisture from any source can have a noticeable affect on nylon filament brush tool performance. Moisture affects filament stiffness and thereby tool aggressiveness. Nylon 6,12 retains stiffness better than other nylon materials and is 2-3 times stiffer than other types of nylon in high humidity or when saturated with oils, solvents or when water is present. In all abrasive filled polymeric filaments, as the degree of abrasive loading increases, the tensile strength and flex fatigue resistance tend to decrease, due to insufficient binding of abrasive and polymer. Bending modulus for a filament can be simply defined as the resistance to bending. This is an inherent characteristic of the polymer used for the abrasive filament. Bending modulus is generally independent of the filament diameter, and since the bending modulus of a family of abrasive filaments made from the same polymer will be the same, the main characteristics which affect filament stiffness are the diameter and length of the filament. The abrasive cutting ability of abrasive-filled nylon filaments exhibits the distinct characteristic of cutting relatively well at the onset of the operation, followed by clear loss of abrasive action within about 1 hour. FIG. 7 shows the degradation in cutting ability of abrasive-filled nylon filaments, filled with a typical aluminum oxide abrasive, when the filaments are attached to a hub to form a brush and the hub rotated so that the filaments strike (and therefore abrade) a stationary workpiece. FIG. 7 represents the cut obtained on a flat carbon steel (1018) plate as a function of time at a constant load of 1.36 Kg. Equipment is typically designed to reverse the brush operation to restore the abrasive action to its original level of activity. An abrupt increase in cut can be achieved if the brush is "dressed", for example, by operating the brush against a wire screen. This is shown at 2 hours 15 minutes in FIG. 7. Another problem associated with abrasive-filled nylon filaments is their poor flex fatigue resistance. Over extended periods of operation the filaments tend to break near the point of attachment to the hub, an inconvenience to the user, resulting in decreased life and economic value of the brush. The present invention addresses some of the problems mentioned above with abrasive-filled nylon and other filaments by presenting a composite abrasive filament comprising a preformed core coated with an abrasive-filled thermoplastic elastomer. This approach centers on the idea that a preformed core coated with an abrasive sheath has a higher initial bending modulus, a more constant bending modulus as a function of time, temperature, humidity and chemical environment, and higher tensile strength than an abrasive-filled thermoplastic filament. Composite abrasive filaments may allow for up to twice the loading of abrasive grains into the thermoplastic elastomer coating without exhibiting significantly reduced flex fatigue resistance compared with abrasive-filled nylon filaments. Much higher levels of initial and continued abrasive action were observed than would have been expected from the increase in abrasive loading. This behavior relates to the compositional nature of the thermoplastic elastomers as well as to the method of preparation of the composite abrasive filaments. Experimentation with and production of abrasive filaments has a long history. Representative of the state of the art are U.S. Pat. Nos. 2,328,998; 2,643,945; 2,793,478; 2,920,947; 3,146,560; 3,260,582; 3,522,342; 3,547,608; 3,669,850; 3,696,563; 3,854,848; 4,097,246; 4,172,440; 4,507,361; 4,627,950; 4,585,464; 4,866,888; and 5,068,142. other references include French Patent Application No. 2,624,773, and EPO publication 0 282,243. The present invention is concerned with composite abrasive filaments comprising preformed cores at least partially coated with abrasive-filled thermoplastic elastomer compositions, which have the unexpected properties of allowing up to twice the loading of abrasive grains into the binding polymeric sheath while exhibiting many times the flex fatigue life compared to previously known filaments. Much higher levels of abrasive action were observed than would have been expected from the simple increase in abrasive loading. Thermoplastic elastomers are defined and reviewed in Thermoplastic Elastomers. A Comprehensive Review, edited by N.R. Legge, G. Holden and H.E. Schroeder, Hanser Publishers, New York, 1987, (referred to herein as "Legge et al."). Thermoplastic elastomers (as defined by Legge et al. and used herein) are generally the reaction product of a low equivalent weight polyfunctional monomer and a high equivalent weight polyfunctional monomer, wherein the low equivalent weight polyfunctional monomer is capable on polymerization of forming hard a segment (and, in conjunction with other hard segments, crystalline hard regions or domains) and the high equivalent weight polyfunctional monomer is capable on polymerization of producing soft, flexible chains connecting the hard regions or domains. This type of material has not been suggested for use in abrasive filaments. "Thermoplastic elastomers" differ from "thermoplastics" and "elastomers" (a generic term for substances emulating natural rubber in that they stretch under tension, have a high tensile strength, retract rapidly, and substantially recover their original dimensions) in that thermoplastic elastomers, upon heating above the melting temperature of the hard regions, form a homogeneous melt which can be processed by thermoplastic techniques (unlike elastomers), such as injection molding, extrusion, blow molding, and the like. Subsequent cooling leads again to segregation of hard and soft regions resulting in a material having elastomeric properties, however, which does not occur with thermoplastics. Some commercially available thermoplastic elastomers include segmented polyester thermoplastic elastomers, segmented polyurethane thermoplastic elastomers, segmented polyurethane thermoplastic elastomers blended with other thermoplastic materials, segmented polyamide thermoplastic elastomers, and ionomeric thermoplastic elastomers. "Segmented thermoplastic elastomer", as used herein, refers to the sub¬ class of thermoplastic elastomers which are based on polymers which are the reaction product of a high equivalent weight polyfunctional monomer and a low equivalent weight polyfunctional monomer. "Ionomeric thermoplastic elastomers" refers to a sub-class of thermoplastic elastomers based on ionic polymers (ionomers). Ionomeric thermoplastic elastomers are composed of two or more flexible polymeric chains bound together at a plurality of positions by ionic associations or clusters. The ionomers are typically prepared by copolymerization of a functionalized monomer with an olefinic unsaturated monomer, or direct functionalization of a preformed polymer. Carboxyl-functionalized ionomers are obtained by direct copolymerization of acrylic or methacrylic acid with ethylene, styrene and similar comonomers by free-radical copolymerization. The resulting copolymer is generally available as the free acid, which can be neutralized to the degree desired with metal hydroxides, metal acetates, and similar salts. Composite abrasive filaments of the present invention comprising preformed cores and abrasive-filled thermoplastic elastomer coatings produce much higher levels of initial cut, maintain their higher cutting ability once an equilibrium condition has been achieved, and are much more resistant to flex fatigue failure than abrasive-filled nylon filaments. SUMMARY OF THE INVENTION The present invention overcomes or reduces many of the problems associated with previously known abrasive filaments. In accordance with the present invention, a composite abrasive filament is presented which includes at least one preformed core at least partially coated with a thermoplastic elastomer having abrasive particles dispersed and adhered therein, the thermoplastic elastomer and abrasive particles together comprising a hardened composition. It is considered within the scope of the invention to include more than one thermoplastic elastomer in the hardened composition. As used herein the term "hardened" refers to the physical state of the thermoplastic elastomer when the temperature of the thermoplastic elastomer is below the melting or dissociation temperature of the hard regions (segmented thermoplastic elastomers) or ionic clusters (ionomeric thermoplastic elastomers), as determined through standard tests such as American Society of Testing Materials (ASTM) test D2117. The term can also be used describe the room temperature (i.e. about 10 to about 40°C) hardness (Shore D scale) of the thermoplastic elastomer. It is preferred that the room temperature Shore D durometer hardness of the thermoplastic elastomers used in the invention be at least about 30, more preferably ranging from about 30 to about 90, as determined by ASTM D790. The term is not meant to include physical and/or chemical treatment of the thermoplastic elastomer/abrasive particle mixture to increase its hardness. As used herein the term "composite abrasive filament" means an abrasive filament having the hardened composition above described over at least a portion, preferably over the entire surface of at least one preformed core, where the ratio of the cross-sectional area of the hardened composition to that of the preformed core ranges from about 0.5: 1 to about 300: 1. preferably from about 1:1 to about 10: 1, more preferably from about 1:1 to about 3:1, the cross-sections defined by a plane perpendicular to the composite abrasive filament major axis. The composite abrasive filaments can be of any length desired, and can of course be round, oval, square, triangular, rectangular, polygonal, or multilobal (such as trilobal, tetralobal, and the like) in cross- section. "Preformed core", as used herein, means one or more core elements which are formed in a step separate from and prior to one or more coating steps, one of which coats the preformed core with abrasive-filled thermoplastic elastomer; in other words, a preformed core is not made simultaneously with the hardened composition. The cross-section of the preformed core is not limited as to shape; however, preformed cores having substantially round or rectangular cross-sections have been found suitable. The preformed core can be continuous individual metallic wires, a multiplicity of continuous individual metallic wires, a multiplicity of non- metallic continuous filaments, or a mixture of the latter two. Preferred preformed cores include single and multistranded metallic cores, e.g., plain carbon steels, stainless steels, and copper. Other preferred preformed cores include a multiplicity of non-metallic filaments e.g., glass, ceramics, and synthetic organic polymeric materials such as aramid, nylon, polyester, and polyvinyl alcohol. Segmented thermoplastic elastomers are preferably the condensation reaction product of a high equivalent weight polyfunctional monomer having an average functionality of at least 2 and an equivalent weight of at least about 350, and a low equivalent weight polyfunctional monomer having an average functionality of at least about 2 and an equivalent weight of less than about 300. The high equivalent weight polyfunctional monomer is capable on polymerization of forming a soft segment, and the low equivalent weight polyfunctional monomer is capable on polymerization of forming a hard segment. Segmented thermoplastic elastomers useful in the present invention include polyester TPEs, polyurethane TPEs, polyimide TPEs, and silicone elastomer/polyamide block copolymeric TPEs, with the low and high equivalent weight polyfunctional monomers selected appropriately to produce the respective TPE. The segmented TPEs preferably include "chain extenders", low molecular weight (typically having an equivalent weight less than 300) compounds having from about 2 to 8 active hydrogen functionality, and which are known in the TPE art. Particularly preferred examples include ethylene diamine and 1,4-butanediol. Blends of TPE and thermoplastic materials are also within the invention, allowing even greater flexibility in tailoring mechanical properties of composite abrasive filaments of the invention. Another aspect of the invention is an abrasive article comprising at least one type of composite abrasive filament, preferably mounted to a substrate such as a hub adapted to be rotated at a high rate of revolution, the filaments comprising a preformed core at least partially coated with thermoplastic elastomer having abrasive particles dispersed and adhered therein, the thermoplastic elastomer and abrasive particles together comprising a hardened composition. A further aspect of the invention is a method of making a composite abrasive filament (as above described), the method including the steps of: (a) rendering a TPE molten and combining abrasive particles therewith; (b) coating at least a portion of a preformed core with a coating comprising the molten thermoplastic elastomer and abrasive particles; and (c) cooling the coating to a temperature sufficient to harden the molten thermoplastic elastomer and thus form the hardened composition. Preferred are methods wherein the TPE is segmented, wherein an extruder is used to render the TPE molten, and wherein the preformed core is stranded metallic or stranded non-metallic material. As used herein the term "molten" means the physical state of the TPE when it is heated to a temperature at least above the dissociation temperature of the hard regions or ionic clusters of the TPE under high shear mixing conditions. BRIEF DESCRIPTION OF THE DRAWING FIGS. 1-4 each show an enlarged perspective view of one of four embodiments of composite abrasive filaments in accordance with the present invention, each having a portion of its abrasive-filled TPE hardened composition removed to show the preformed core; FIG. 5 shows a perspective view of one embodiment of a brush tool (in this case a rotary brush tool) incorporating composite abrasive filaments in accordance with the invention; FIG. 6. is a cross-sectional view (reduced) of an extrusion die, with molten, abrasive-filled TPE and preformed core shown in phantom; FIG. 7 is a bar graph which reveals the weight in grams removed from a workpiece (also referred to in the art as "cut") as a function of time for a rotating brush tool having a plurality of prior art nylon abrasive filaments; FIGS. 8, 11, 13, 15, 21 and 23 are bar graphs showing test results comparing the amount of 1018 steel plate removed as a function of time by brushes employing prior art nylon abrasive filaments with brushes employing composite abrasive filaments in accordance with the present invention; FIGS. 9, 12, 14, 16, 22 and 24 are bar graphs similar to FIGS 8, 11, 13, 15, 21, and 23, respectively, comparing the amount of 1008 steel perforated screen removed; FIG. 10 is a graph which shows the effect of increased abrasive loading in TPE coatings of the composite abrasive filaments of the invention on the ability of rotating brushes incorporating same to abrade steel plate and screen; FIGS. 17-20 are bar graphs which show comparative abrasion test results of rotating brushes which include composite abrasive filaments of the invention in brushes, the filaments having various types of abrasive particles in the hardened composition; and FIGS. 25-28 are bar graphs which show test results of workpiece removed as a function of power level for cylindrical brushes incorporating composite abrasive filaments in accordance with the present invention. DESCRIPTION OF PREFERRED EMBODIMENTS Composite Abrasive Filament Embodiments Four embodiments 10, 20, 30, and 40 of composite abrasive filaments in accordance with the present invention are illustrated in enlarged perspective views in FIGS. 1-4, where in each embodiment it will be appreciated that a portion of the hardened composition comprising TPE and abrasive particles has been removed to show the preformed cores. FIG. 1 shows an enlarged perspective view of composite abrasive filament 10, having a preformed core 12 partially covered by a hardened composition 14 of TPE and abrasive particles 18. Preformed core 12 in this embodiment is a 1 x 7 stranded preformed core, formed for example from seven individual stainless steel wires 16. The TPE of the hardened composition 14 has dispersed throughout and adhered therein a plurality of abrasive particles 18, such as aluminum oxide abrasive particles. FIG. 2 shows an alternate composite abrasive filament embodiment, wherein the preformed core 12a is formed from a plurality of parallel, continuous metallic wires or non-metallic monofilaments 16a, while FIG. 3 shows a second alternate embodiment, wherein the preformed core 12b is a cable having 3 7 arrangement of three strands 16b, the strands in turn being each 1 x 7 strands of seven individual metallic wires or non-metallic monofilaments as in FIG. 1. The composite abrasive filaments 20 and 30 each have a hardened composition 14 of thermoplastic elastomer having abrasive particles 18 dispersed and adhered therein partially covering preformed cores 12a and 12b, respectively. Regarding the embodiment shown in FIG.2, it should be noted that the hardened composition can be between the parallel monofilaments of the preformed core, so that the individual monofilaments equally or unequally spaced apart. FIG. 4 shows an enlarged perspective view of another composite abrasive filament embodiment in accordance with the present invention. Preformed core 12c is this embodiment is a single continuous wire or monofilament of, for example, stainless steel or glass fiber. As with previous embodiments, core 12c has thereon a hardened composition 14 of TPE having dispersed and adhered therein a plurality of abrasive particles 18. Preformed core diameters for composite abrasive filaments of the present invention used on typical hand-held tools are preferably at least about 0.1 mm, while the composite abrasive filaments themselves preferably have a diameter ranging from about 1.0 mm to about 2.0 mm. Composite abrasive filaments of the invention having a diameter ranging from about 0.75 mm to about 1.5 mm have an ultimate breaking force (measured using a standard tensile tester known under the trade designation "Instron" Model TM, according to the test described below) of at least about 2.0 kg, a 50% fatigue failure resistance (i.e. the time require for 50% of the filaments in a given brush to detach from the brush at given conditions) of at least about 15 minutes; and an abrasion efficiency (i.e. weight of workpiece removed per weight of filament lost) on cold rolled steel (1018) plate of at least about 2. As may be seen by the examples herein below, balancing these preferences may be workpiece dependent. Thermoplastic Elastomers Segmented TPEs useful in the composite abrasive filaments of the present invention generally and preferably comprise the reaction product of a high equivalent weight polyfunctional monomer having a functionality of at least about 2 and an equivalent weight of at least about 350 adapted to form a soft segment upon polymerization, and a relatively low equivalent weight polyfunctional monomer having a functionality of at most about 2 and an equivalent weight of at most about 300, adapted to form a hard segment upon polymerization. Chain extenders are typically used in segmented thermoplastic elastomers to increase the hard segment and hard domain size and thus provide one mechanism to alter the physical properties of the resultant segmented TPE. Chain extenders useful in the segmented TPEs of the present invention preferably have an active hydrogen functionality ranging from about 2 to 8, preferably from about 2 to 4, and more preferably from about 2 to 3, and an equivalent weight less than about 300, more preferably less than about 200. Well suited chain extenders are the linear glycols such as ethylene glycol, 1,4- butanediol, 1,6-hexanediol, and hydroquinone bis(2-hydroxyethyl) ether. Segmented TPEs useful in the composite abrasive filaments of the present invention preferably comprise segmented polyester TPEs, segmented polyurethane TPEs, and segmented polyamide TPEs. The low and high equivalent weight polyfunctional monomers are variously chosen to produce one of the above segmented TPEs. For example, if the TPE comprises a segmented polyester, such as the segmented copoly(etherester)s, the low and high equivalent weight polyfunctional monomers are preferably poly(tetramethylene terephthalate) and poly (tetramethylene oxide), respectively. If the TPE comprises a segmented polyurethane, the low equivalent weight polyfunctional monomer is preferably a polyfunctional isocyanate and the high equivalent weight polyfunctional monomer is preferably a polyfunctional amine. The weight percent of low equivalent weight polyfunctional monomer in the total weight of monomers which react to produce segmented TPEs preferably ranges from about 20 to about 60 percent, more preferably ranging from about 20 to about 40 percent. Ionomers useful in forming ionomeric TPEs typically and preferably comprise the reaction product of a functionalized monomer with an olefinic unsaturated monomer, or comprise a polyfunctionalized preformed polymer. Within the terms "ionomeric TPEs" and "ionomers" are included anionomers, cationomers, and zwitterionomers. TPEs (segmented and ionomeric) useful in composite abrasive filaments of the invention preferably have Shore D durometer hardness values ranging from about 30 to about 90, more preferably ranging from about 50 to about 80. The mechanical properties of segmented thermoplastic elastomers (such as tensile strength and elongation at break) are dependent upon several factors. The proportion of the hard segments in the polymers which form the TPEs, their chemical composition, their molecular weight distribution, the method of preparation, and the thermal history of the TPE all affect the degree of hard domain formation. Increasing the proportion of the low equivalent weight polyfunctional monomer tends to increase the hardness and the modulus of the resultant TPE while decreasing the ultimate elongation. The upper use temperature of segmented TPEs is dependent upon the softening or melting point of the low equivalent weight polyfunctional monomer comprising the hard segments. For long term aging, the stability of the high equivalent weight polyfunctional monomer comprising the soft segment is also important. At elevated temperatures and with a lower percentage of hard segments which can contribute to hard domains, bending modulus and tensile strength of the TPE are generally reduced. Preferred TPEs having the above properties and useful in the invention include those formed from segmented polyesters represented by general formula I and mixtures thereof wherein: d and e are integers each ranging from about 2 to about 6, and wherein d and e may be the same or different, but not differing by more than 1 integer; and x and y are integers selected so that the resulting segmented polyester TPE has a Shore D durometer hardness ranging from about 30 to about 90. Total molecular weight (number average) of segmented polyesters within general formula I ranges from about 20,000 to about 30,000; x ranges from about 110 to about 125; and y ranges from about 30 to about 115, more preferably from about 5 to about 70. Preferred ionomers used to form ionomeric TPEs useful in the invention comprise the copolymerization reaction product of a functionalized monomer and an olefinic unsaturated monomer, the ionomers being represented by general formula II R , R-= " CH CH j - C H 9 C-)- • R - C U D m n - + D It and mixtures thereof wherein: R 1 , R 9 , and R * **l which may be the same or different and are selected from the group consisting of hydrogen, alkyl, substituted alkyl, aryl, and substituted aryl; m and n are integers which may be the same or different which are selected so that the weight percentage of the functionalized monomer ranges from about 3 to about 25 weight percent of the total ionomer weight and so that the resulting ionomeric TPE has a Shore D durometer ranging from about 30 to about 90; D is a functional group selected from the group consisting of Coo M is selected from the group consisting of Na, Zn, K, Li, Mg, Sr, and Pb. Particularly preferred are those ionomers represented by general formula II wherein R 1 = R 2 = R 3 = CH3 and D = COO. A particularly preferred ionomer is when R 1 = CH3, D ■= COO, and M = Na, such an ionomer being commercially available, for example that known under the trade designation "Surlyn 8550" (du Pont). The values of m and n are normally not given by manufacturers but are selected to provide the resulting ionomeric TPE with a room temperature Shore D durometer ranging from about 30 to about 90. Alternatively, m and n may be characterized as providing the molten ionomeric TPE with a flow rate (formerly termed "melt index" in the art) ranging from about 1 gm/10 mins to about 10 gms/10 mins (as per ASTM test D1238-86, condition 190/2.16, formerly D1238-79, condition E). Briefly, the test involves placing a sample within the bore of a vertical, heated cylinder which is fitted with an orifice at the bottom of the bore. A weighted piston is then placed within the cylinder bore, and the amount in grams of molten polymer exiting the cylinder through the orifice is recorded in grams for a 10 minute period. The functionalized monomer may be selected from acrylic acid, methacrylic acid, vinyl acetate, and the like, and copolymers thereof, with acrylic and methacrylic acid particularly preferred. The olefinic monomer may be selected from ethylene, propylene, butadiene, styrene, and the like, and copolymers thereof, with ethylene being the olefinic monomer of choice due to its availability and relatively low cost. The functionalized monomer and olefinic monomer are typically and preferable directly copolymerized using free radicals, such methods being well known in the art and needing no further explanation herein. Particularly preferred segmented polyamides useful in making segmented polyamide TPEs useful in the invention are those segmented polyamides represented by general formula III and mixtures thereof, wherein: PA = a difunctional polyamide having equivalent weight less than about 300; PE ■= a dihydroxypolyether having equivalent weight of at least 350 and comprising polymers selected from the group consisting of dihydroxypolyoxyethylene, dihydroxypolyoxypropylene, and dihydroxypolyoxytetramethylene; and z = an integer selected to provide the resulting segmented polyamide TPE with a Shore D durometer hardness ranging from about 30 to about 90. Segmented polyamides within formula III are commercially available, such as those known under the trade designation "Pebax", available from Atochem Group of Elf Aquitaine, with the 63 and 70 Shore D durometer versions being particularly preferred in the present invention. Although values of z are proprietary to the manufacturers, and polymers within general formula III may be characterized according to hardness, they may alternatively be characterized according to their melt flow rate (as described above), with values ranging from about 1 cjm/10 min to about 10 cjm/10 min being preferred (ASTM 1238-86, 190/2.16). Particularly preferred segmented polyurethanes useful in making polyurethane TPEs useful in the invention are those segmented polyurethanes represented by general formula IV and mixtures thereof wherein: polyol = a polyester polyol or polyether polyol having an average molecular weight ranging from about 600 to about 4000; and t = an integer selected to provide the resulting segmented polyurethane TPE with a Shore D durometer hardness ranging from about 30 to about 90. The value of "t" is chosen relative to the molecular weight of the polyol to give a range of molecular weights; typically and preferably, the number average molecular weight of segmented polyurethanes represented by general formula IV ranges from about 35,000 to about 45,000. In general, segmented polyurethanes may be made by mixing the first and second polyfunctional monomers and chain extender together at temperatures above about 80°C. Preferably, the ratio of isocyanate functional groups to isocyanate reactive groups ranges from about 0.96 to about 1.1. Values below about 0.96 result in polymers of insufficient molecular weight, while above about 1.1 thermoplastic processing becomes difficult due to excessive crosslinking reactions. As mentioned previously, blends of TPEs and other polymers have also proven useful, such as the polyurethane/acrylonitrile-butadiene-styrene blends known under the trade designation "Prevail", grades 3050, 3100, and 3150, all from Dow Chemical. Grade 3050 has a melt flow rate (ASTM-1238-86, 230/2.16) of 26 gm/10 min, and a Shore D hardness of about 62. Block copolymers regarded by those skilled in the plastics processing art as TPEs, including the elastomeric copolymers of silicones and polyimides, may also prove useful in composite abrasive filaments of the invention. Commercially available elastomeric copolymers of thermoplastic silicones and polyimides include those known under the trade designation "Siltem STM- 1500", from GE Silicones. Each of the polymers within formulas I-IV as shown above are now discussed in greater detail. Segmented Polyesters As noted above, if the TPE is based on a segmented polyester, such as the segmented copoly(etherester) as shown in formula I, the low and high equivalent weight polyfunctional monomers are preferably based on poly(tetramethylene terephthalate) which forms the hard segment upon polymerization and poly(tetramethylene oxide) which forms the soft segment upon polymerization, respectively. The poly(ether) component of the copoly(etherester) is preferably derived from α-hydro-ω- hydroxyoligo(tetramethylene oxide) of number average molecular weight ranging from about 1,000 to about 2,000. The copoly(ester) component of the copoly(etherester) is preferably based on poly(tetramethylene terephthalate) which forms hard segments upon polymerization, having average molecular weights ranging from about 600 to about 3,000. The molecular weight for copoly(etherester) polyesters within formula I preferably ranges from about 20,000 to about 40,000. Ionomers Ionomers which may behave as ionomeric TPEs and thus useful in the present invention, such as those ionomers known under the trade designation "SURLYN" (formula II), are preferably prepared by copolymerization of a functionalized monomer and an olefinic unsaturated monomer, or by direct functionalization of a preformed polymer, as previously noted. Ionomers within formula II are particularly preferred for forming ionomeric TPEs for use in hardened compositions in composite abrasive filaments of the invention. The large quantities of commercial quality ethylene/methacrylic acid copolymers, for example containing between about 5 and about 20 weight percent methacrylic acid component, makes these ionomers particularly useful in the present invention. M in formula II is typically and preferably chosen from sodium (Na) and zinc (Zn), although ionomers using potassium (K), lithium (Li), magnesium (Mg), strontium (Sr) and lead (Pb) are considered within the scope of formula II. Segmented Polyamides Polyamides within formula III and useful forming segmented polyamide TPEs for use in the invention are typically described as polyether block amides (or "PEBA"), wherein the latter may be obtained by the molten state polycondensation reaction of dihydroxypolyether blocks and dicarboxylic acid- based polyamide blocks as shown in formula III (wherein PA represents "polyamide" and PE represents "polyether"). Dicarboxylic polyamide blocks may be produced by the reaction of polyamide precursors with a dicarboxylic acid chain limiter. The reaction is preferably carried out at high temperature (preferably higher than 230 °C) and preferably under pressure (up to 2.5 Mpa). The molecular weight of the polyamide block is typically controlled by the amount of chain limiter. The polyamide precursor can be selected from amino acids such as aminoundecanoic acid and aminododecanoic acid; lactams, such as caprolactam, lauryl lactam, and the like); dicarboxcylic acids (such as adipic acid, azelaic acid, dodecanoic acid, and the like); and diamines (such as hexamethylene diamine, dodecamethylene diamine, and the like). The dihydroxypolyether blocks may be produced from polyether precursors by either of two different reactions: an ionic polymerization of ethylene oxide and propylene oxide to form dihydroxypolyoxyethylene and dihydroxypolyoxypropylene polyether precursors; and cationic polymerization of tetrahydrofuran for producing dihydroxypolyoxytetramethylene polyether precursors. The polyether block amides are then produced by block copolymerization of the polyamide precursors and dihydroxypolyether precursors. The block copolymerization is a polyesterification, typically achieved at high temperature (preferably ranging from 230 to 280 °C) under vacuum (10 to 1,400 Pa) and the use of an appropriate catalyst such as Ti(OR) , where R is a short chain alkyl. It is also generally necessary to introduce additives such as an antioxidant and/or optical brighteners during polymerization. The structure of the resulting polyether block amides comprises linear, regular chains of rigid polyamide segments and flexible polyether segments. Since polyamide and polyether segments are not miscible polyether block amides such as those represented by formula m present a "biphasic" structure wherein each segment offers its own properties to the polymer. Segmented Polyurethanes Segmented polyurethane TPEs useful in the present invention are preferably formed from segmented polyurethanes within formula IV, which are comprised of a high equivalent weight polyfunctional monomer and a low equivalent weight polyfunctional monomer as above described, and may also include a low molecular weight chain extender, also as above described. In thermoplastic polyurethane elastomers, the hard segment is formed by addition of the chain extender, for example, 1,4-butane diol, to a diisocyanate, for example, 4,4'-diphenylmethane diisocyante (MDI). The soft segment consists of long, flexible polyether or polyester polymeric chains which connect two or more hard segments. At room temperature, the low melting soft segments are incompatible with the polar, high melting hard segments, which leads to a microphase separation. Polyurethanes useful in forming segmented polyurethane TPEs are generally made from long chain polyols having an average molecular weight ranging from about 600 to 4,000 (high equivalent weight polyfunctional monomer), chain extenders with a molecular weight ranging from about 60 to about 400, and polyisocyanates (low equivalent weight polyfunctional monomer). Preferred long chain polyols are the hydroxyl terminated polyesters and the hydroxyl terminated polyethers. A preferred hydroxyl terminated polyester is made from adipic acid and an excess of a glycol such as ethylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, or mixtures of these diols. Long chain polyether polyols useful in making polyurethanes within formula IV useful in making segmented polyurethane TPEs useful in composite abrasive filaments of the invention are preferably of two classes: the poly(oxypropylene)glycols and the poly(oxytetramethylene)glycols. The former glycols may be made by the base catalyzed addition of propylene oxide and/or ethylene oxide to bifunctional initiators, for example, propylene glycol or water, while the latter may be made by cationic polymerization of tetrahydrofuran. Both of these classes of polyethers have a functionality of about 2. The mixed polyethers of tetrahydrofuran and ethylene or propylene oxide may also be effectively used as the soft segment in the polyurethane TPE. In contrast to other polyurethanes, only a few polyisocyanates are suitable for producing thermoplastic elastomer polyurethanes. The most useful preferred polyisocyanate is MDI, mentioned above. Others include hexamethylene diisocyanate (HDI), l-isocyanato-3-isocyanatomethyl-3,5,5- trimethylcyclohexane (IPDI); 2,4 and 2,6-toluene diisocyanate (TDI); 1,4 benzene diisocyanate, and trans-cyclohexane-l,4-diisocyanate. Preformed Cores Preformed core materials useful in the present invention can be envisioned as an abrasive coating substrate that can be selected or modified in its surface characteristics, mechanical properties, and environmental stability properties. The preformed core material is preferably selected or capable of being modified so that its surface has the ability to achieve adhesion between the core and thermoplastic elastomer coating. Important mechanical properties include tensile strength and flex fatigue resistance while operating under various chemical, thermal and atmospheric conditions. Preformed cores useful in the composite abrasive filaments of the present invention include: metal wire such as stainless steel, copper, and the like; inorganic fibers such as glass and ceramic fibers; synthetic fibers, such as aramid, rayon, and the like; natural fibers such as cotton, and mixtures of these. Although continuous monofilaments may be used, preferred are stranded, cable and yarn versions of these materials. "Stranded" as used herein refers to twisted together wires while "yarn" refers to twisted together non- metallic monofilaments. Typical arrangements include 1 3, 1 x 7, 1 x 19, and 3 x 7 arrangements, wherein the first number refers to the number of strands or yarns and the second number refers to the number of individual monofilaments or wires twisted together in each yarn or strand. "Cable" refers to two or more strands twisted together, while "plied yarns" refers to two or more yarns twisted together, preferably having the opposite direction of twist compared with the cables (for example, if the cables are twisted together "right handed" the plied yarn may be twisted together "left handed"). Alternatively, the performed core may be in the form of untwisted continuous wires or monofilaments. Preferred yarns include yarns of glass fibers, ceramic fibers, aramid fibers, nylon fibers, polyethylene terephthalate fibers, cotton fibers, plied version thereof, and mixtures thereof. The diameter of the preformed core is preferably at least about 0.01 mm, more preferably ranging from about 0.1 mm to about 0.7 mm, although there is actually no upper limit to the diameter other than that imposed by currently known methods of making composite abrasive filaments. Abrasive Particles Abrasive particles are preferably dispersed throughout and adhered within the hardened TPE coating. Abrasive particles useful in the composite abrasive filaments of the present invention may be individual abrasive grains or agglomerates of individual abrasive particles. Suitable agglomerated abrasive particles are described in U.S. Pat. Nos. 4,652,275 and 4,799,939. The abrasive particles may be of any known abrasive material commonly used in the abrasives art. Preferably, the abrasive particles have a hardness of greater than about 7 Mohs, most preferably greater than about 9 Mohs. Examples of suitable abrasive particles include individual silicon carbide abrasive particles (including refractory coated silicon carbide abrasive particles), fused aluminum oxide, heat treated fused aluminum oxide, alumina zirconia, cubic boron nitride, garnet, pumice, sand, emery, mica, corundum, quartz, diamond, boron carbide, fused alumina, sintered alumina, alpha alumina-based ceramic material. The abrasive particles are preferably present in the hardened TPE coating at a weight percent (per total weight of TPE and abrasive particles) ranging from about 0.1 to about 65 weight percent, more preferably from about 3 to about 60 weight percent. The size of the abrasive particles incorporated into the hardened TPE coating depends on the intended use of the composite filaments. For applications requiring cutting or rough finishing, larger abrasive particles are preferred, while abrasive particles having smaller size are preferred for finishing applications. Preferably, the average diameter of the abrasive particles is no more than about 1/2 the diameter of the composite abrasive filament, more preferably no more than about 1/3 of the diameter of the composite abrasive filament. The surface of the abrasive particles (or a portion of their surface, or a portion of the particles but their whole surface) may be treated with coupling agents to enhance adhesion to and dispersibility in the molten TPE. Examples of suitable coupling agents include silane, zirco-aluminate, and titanate coupling agents. Abrasive Articles Composite abrasive filaments of the invention may be incorporated into a wide variety of brushes, either assembled to form an open, lofty abrasive pad, or attached to various substrates. FIG. 5 shows one embodiment of a wheel brush 50 within the invention having a plurality of composite abrasive filaments 51 glued or otherwise attached to a hub 52. A construction of such a brush is described in "Test Brush Construction π", below. The composite abrasive filaments of the invention can be incorporated into brushes of many types and for myriad uses, such as cleaning, deburring, radiusing, imparting decorative finishes onto metal, plastic, and glass substrates, and like uses. Brush types include wheel brushes, cylinder brushes (such as printed circuit cleaning brushes), mini-grinder brushes, floor scrubbing brushes, cup brushes, end brushes, flared cup end brushes, circular flared end cup brushes, coated cup and variable trim end brushes, encapsulated end brushes, pilot bonding brushes, tube brushes of various shapes, coil spring brushes, flue cleaning brushes, chimney and duct brushes, and the like. The filaments in any one brush can of course be the same or different. Method of Making Composite Abrasive Filaments Composite abrasive filaments in accordance with the present invention can be made by any of a variety of processes, including passing one or more preformed cores through a die in which molten, abrasive-filled TPE is coated onto the preformed cores as they move through the die, spray coating abrasive- filled, molten TPE onto a preformed core, or by passing a preformed core through a bath of molten TPE, followed by applying abrasive particles to the molten TPE coating. (Alternatively, the abrasive particles could be in the bath of molten TPE.) Abrasive particles may be applied to a TPE-coated core by projecting the abrasive grains toward the TPE-coated preformed core by force, such as electrostatic force. However, the preferred method is the first mentioned one, wherein one or more preformed cores are passed through a die which at least partially coats the preformed cores with molten, abrasive-filled TPE, and the molten TPE cooled to form the hardened composition. In one preferred method in accordance with the invention, a die 60 such as that shown in FIG. 6 is attached to the exit of an extruder, an extruder being one preferred technique of rendering the TPE molten and mixing the abrasive particles into the molten TPE. The apparatus and method of Nungesser et al. , U.S. Pat. No. 3,522,342, is one preferred method. FIG. 6 shows molten, abrasive-filled TPE (or abrasive-filled TPE/ thermoplastic polymer blend, as desired) in phantom at 62, and a single preformed core 61, also in phantom, it being recognized by those skilled in the art that the polymer melt and preformed core flow from left to right as shown. The abrasive-filled, TPE- coated preformed core 63 exits die 60 as shown. Shown at 64 is a screw attachment for attaching the die to an extruder (not shown). Suitable modifications to die 60 may be made to pass a plurality of preformed cores, these modifications being within the skill of the artisan. For each TPE the zone temperatures of the extruder and die temperature are preferably set at the temperatures commercially recommended for each TPE (see Table A), the main limitation being the melting or dissociation temperature of the hard domains or ionic clusters of the TPE. Preferred extruder zone and die temperatures are listed in Table A. The extruder (or other TPE melt rendering means, such as a heated vessel and the like) preferably heats the TPE above the hard domain or ionic cluster melting or dissociation temperature (which may have a range that can change with type and grade of the TPE) and pushes molten TPE through a heated die. Abrasive particles may be added to the molten TPE through a feed port in the extruder into the molten TPE mass, preferably at point early enough to afford adequate dispersal of abrasive particles throughout the molten TPE. Alternatively, abrasive particles may be distributed in the molten TPE coating via a second step (i.e. after the preformed core has been coated with molten TPE), such as by electrostatic coating. TABLEA 1 ; EXTRUDER ZONEANDDIETEMPERATURES. °C 1 Data from Legge, et al. 2 "1" corresponds to first heated zone, while "4" refers to the zone preceding the die Lower temperature for lower hardness, higher temperature for higher hardness grades Higher temperature near zone 41 lower temperature near outlet of die. A cold water quench is located immediately downstream of the die through which the molten TPE-coated preformed core passes to achieve rapid cooling of the molten TPE to form a hardened composition comprising TPE and abrasive particles on the preformed core prior to windup of the coated preformed core onto a windup roll. A process wherein multiple preformed cores are coated simultaneously may be preferably from the standpoint of mass producing composite abrasive filaments, which may be accomplished using a manifold arrangement. In this case, more than one wind up roll may be required. Conventional dies may require a pulley mechanism having vertical and horizontal adjustments placed immediately downstream of the cold water quench to provide means for centering the preformed core in the die and provide concentric coatings, of late, commercially available dies provide this centering function without the use of a separate mechanism. A die known under the trade name "LOVOL", available from Genca Die, Clearwater, Florida, having four helicoid fixed center arrangement, gives acceptable abrasive particle dispersion in the molten TPE, substantially concentric coatings, and is easier to rethread with preformed core material when preformed core material is changed. The abrasive-filled TPE coating thickness may be changed using mechanical inserts into the die. Thickness of the coating may also be adjusted somewhat by the speed that the preformed core passes through the die, higher speeds yielding somewhat thinner TPE coatings. A preformed core speed of ranging from about 30 to about 100 re/min has proved preferable, more preferably from about 30 to about 45 re/min, for pilot scale operations, while production speeds may be considerably higher, such as 300 re/min in large scale operations. The hardened, abrasive-filled TPE-coated preformed core may be cut to individual composite abrasive filaments having the desired length. There is no need to orient the filaments to increase their tensile strength prior to use. More detailed descriptions of the method of fabricating composite abrasive filaments and methods of abrading flat plate and flat screen workpieces, along with performance test results, are given in the Examples which follow. EXAMPLES The following examples are given as illustrations of the invention and are not intended as limitations thereof. In all examples, all parts and percentages are by weight unless otherwise stated. "P" refers to heat treated abrasive particles where used in conjunction with an abrasive particle designation, while the "grade" of abrasive particles refers to that used by the Grinding Wheel Institute (ANSI ASC B74.18-1984). "CRS" refers to "cold rolled steel". TEST METHODS Fatigue Failure Resistance This test was used to evaluate fatigue failure of composite abrasive filaments, the results of which can be used to predict relative usable life of a brush made from the composite abrasive filaments of the invention. The test procedure used was published and described in Technical Bulletin No. 6, "Fatigue Resistance and Some of the Factors That Affect Flex Life of Brush Filling Materials", February, 1978, by du Pont, Plastic Products and Resins Department, Code # E-19743. The test procedure was followed exactly, with the exception that the filament holding device on the tester was changed to four chucks, each of which could be adjusted to firmly grasp one composite abrasive filament. In this test, the four chucks were affixed to a drive shaft, each of which was used to secure an individual composite abrasive filament or control filament. The chucks were mounted 90° apart with each being spaced 50 mm from the center of the drive shaft. The drive shaft was operated at 500 rpm. As per the test procedure, the interference between the filaments and the impact bar was adjusted, depending upon the filament diameter. For a 1.02 mm diameter filament, the interference was 12.22 mm; for 1.14 mm filament, the interference was 13.21 mm; for a 1.27 mm filament, the interference was 16.51; and for a 1.40 mm filament, the interference was adjusted to 18.16 mm. After securing four identical test filaments to the drive shaft, the drive shaft was rotated and the time required to cause 50% of the filaments to break was recorded. This value is reported in Table 4 for Examples 1-27 and Comparative Examples A-F. Test Brush Construction I Composite abrasive filaments were used to form abrasive brushes by attaching one end of the composite abrasive filaments to a cast aluminum, machined, two-part hub. The first part of the cast aluminum, machined hub consisted of a 5 mm thick aluminum disc having a 32 mm center hole, a 102 mm outside diameter, and had a raised square cross-sectional surface at the periphery that was raised 4 mm. The second part of the cast aluminum hub was machined from a 19 mm thick cast aluminum disc, also having a 32 mm center hole with a 102 mm outside diameter. The second part of the cast aluminum hub was machined to be 5 mm thick, with the exception of three circular raised surfaces on one side of the disc, each concentric with the center hole: an outer, an intermediate, and an inner circular raised surface, all three raised circular surfaces parallel to the disc major surfaces. The outer circular raised surface had a square cross-section of 4 mm by 4 mm and an outside edge diameter of 102 mm. The intermediate circular raised surface had an outside edge diameter of 73 mm and an inside edge diameter of 68 mm, and was raised 13 mm above the disc major surface. The annulus formed by one of the disc major surface and the intermediate raised surface was machined to produce eight equally sized and spaced bores extending radially through the annulus, each bore being 9 mm in diameter with the spacing between adjacent bores being about 3 mm. These bores defined holes into which composite abrasive filaments were subsequently placed. The inner circular, raised surface had an inside edge diameter of 32 mm which, when the two hub parts were mated, defined the center hole of the hub. The inner raised surface oiiter edge had a diameter (measured from the hub center) of 44 mm and was raised 13 mm above the disc major surface. The inner raised surface and intermediate raised surface of the second hub disc defined the plane against which the first hub part was placed. The raised square cross sections of the first and second hub parts opposed each other. One end of approximately 125 to 150 composite abrasive filaments, each 83 mm long, were placed into each of the eight bores. Sufficient number of filaments were placed in each bore to essentially fill each bore. A two-part epoxy adhesive liquid resin composition (combination of the epoxy "Epi-Rez" WD-510, from Rhone-Poulenc, and the amine "Jeffamine" D-230, available from Texaco Chemical Company, Bellaire, Texas) was placed over the filament end which protruded into the bore. The first part of the machined aluminum hub was secured to the second part using four screws, 4 mm in diameter, through four holes equally spaced 42 mm from the center of the machined aluminum hub. This caused the composite abrasive filaments to slightly fan out with a resultant filament trim length of about 50 mm. After being held for approximately 24 hours at room temperature (about 25 °C, to allow the epoxy resin to harden), followed by a post cure at about 60°C for about 1 hour, the composite abrasive filament brushes were ready for subsequent evaluations. The brushes had a 32 mm center hole and approximately 200 mm outside diameter. Test Brush Construction II A mold was fabricated so that composite abrasive filaments of the invention could be used to form abrasive brushes as shown in FIG. 5. A round base plate was fabricated with a 3.18 cm diameter center through hole which was adapted to accept a solid, cylindrical core piece having outer diameter slightly less than 3.18 cm. Slots were machined into one surface of the base plate to create a radial pattern so that thin metal spacers could be inserted therein. The slots extended radially, starting from a point about 5 cm from the center through hole and extending to the periphery of the plate. A right cylinder (200 mm I.D.) was then fastened to the surface of the base plate having the slots so that the hole in the base plate and the cylinder were concentric. The spacers were then put in the slots, the solid, cylindrical core piece inserted in the through hole, and a multiplicity of composite abrasive filaments having length equal to the slot length plus about 5 cm were then aligned within the spaces left between the spacers. The spacers provided a method to uniformly and closely distribute the composite abrasive filaments radially with a predetermined length which could then be held firmly with a clamp ring, which fitted over the end of the filaments pointing toward the center through hole. A polymeric cast hub was then formed by pouring a liquid, two-part epoxy resin (trade designation "DP-420", from 3M) into the center cavity formed between the solid, cylindrical center core piece and the clamp ring, at about 50°C. When the resin was fully cured, the brush was removed from the device and then tested in Examples 25-27 and Comparative Example F. Flat Plate Abrasion Tests Composite abrasive filament-containing brushes were weighed and separately mounted on a shaft connected to a 2.24 Kw (3hp) motor which operated at 1750 rpm. 1018 CRS steel plates, 100 mm square by approximately 6 mm thick, were weighed and then brought in contact with each brush with a force of 13.3 Pa. At 15 minute intervals, the test brushes and steel plates were again weighed to determine the weight loss of the steel plates and weight loss of the test brushes. After 8 test periods of 15 minutes each (120 minutes total) the tests were concluded and the total cut (steel plate weight loss) was calculated. This value was divided by 2 to give average grams cut per hour by each brush. The efficiency (η) of the brushes was calculated by dividing the total plate weight loss by the total composite abrasive filament weight loss. Results are reported in Table 4. Perforated Screen Abrasion Tests Brushes were tested for abrasion of perforated steel. In this test, 50 X 150 mm pieces of 16 gauge 1008 CRS steel perforated screen having approximately 4 mm diameter staggered holes with 46% open and having stock pattern number 401, commercially available from Harrington and King Perforating Company, Inc., Chicago, Illinois, were abraded, a double layer of the screen used in each test. Results are reported in Table 4. Composite Abrasive Filament Tensile Strength Composite abrasive filaments of the invention were evaluated for their tensile strength by measuring the force required to break a 100 mm long composite abrasive filament grasped at each end by one of two jaws of a standard tensile tester (known under the trade designation "Instron" Model TM), where the jaws were initially spaced 25 mm apart and then separated at the rate of 50 mm a minute. The force required to break each filament was noted and recorded as kilograms force required. Composite Abrasive Filament Extrusion Various composite abrasive in accordance with this invention were prepared by the melt extrusion process. A twin screw extruder fitted with two 30 mm diameter co-rotating screws having an L/D ratio of 30: 1 (model ZSK- 30, from Werner-Pfleiderer), was employed in each case. The thermoplastic elastomers employed were first rendered molten by the extruder (using zone and die temperatures in Table A above for each TPE), whereupon abrasive particles were controUably added through a feed port of the extruder barrel. Preformed cores of stainless steel, aramid fiber yarn, glass fiber yarn, depending on the Example, were pulled through an extrusion die which allowed the molten abrasive-containing TPE to be coated on the preformed cores. The extrusion die used was commercially available under the trade designation "LOVOL", from Genca Die, Clearwater, Florida. After exiting the extrusion die, the molten TPE was hardened by cooling the coated preformed core in a water stream placed about 150 mm from the face of the extrusion die, after which the abrasive-filled, TPE coated preformed core was wound onto a separate roll for each preformed core/TPE combination. Composite abrasive filaments were subsequently cut from each roll. It is important to note that none of the coated preformed cores produced by the above method required orienting prior to being accumulated on the roll, subsequent cutting into filaments, and fabrication into brush devices. The TPEs employed, including some of their physical properties, are listed in Table 1. Table 2 lists the various preformed cores used, while Table 3 lists the example composite abrasive filaments (Examples 1-27). Table 4 lists Comparative Examples A-F, where TPE, abrasive particle type, size, etc., are tabulated. The abrasive particle content was determined by using a standard thermal burnoff technique. Five abrasive-filled nylon control filaments A-E were used to compare with Examples 1-24, which used Test Brush Construction I, above. The composition of Comparative Example filaments A-E is indicated in Table 4. All Comparative Example filaments A-E were commercially available (under the trade designation "TYNEX") from du Pont except for Comparative Example B filament, which was commercially available from Asahi Chemical Company, Japan. Three brushes were made using Test Brush construction II, and employing composite abrasive filaments comprising blends of polyurethane TPE and ABS terpolymer (Examples 25-27). A "control" Example F was used to verify the abrasion testing. Example F used composite abrasive filaments similar to Example 8A, differing only by employing Test Brush Construction II. The composition of Example F is listed in Table 4, although this filament is within the invention. The results of the abrasion tests described above are presented in Table 5 for the composite abrasive filaments (Examples 1-27) made in accordance with this invention, while Table 6 lists abrasion results for Comparative Example filaments A-F. TABLE 1 TABLE 2 TABLE 3 Table 3 - Continued TABLE 4 I TABLE 5 Table 5 - Continued TABLE 6 Discussion of Results FIG. 8 shows, in bar graph form, the results of workpiece removed as a function of time tests for comparative Examples A and B and Examples 1-3 of the present invention. It is clear that abrasive filament Example A (abrasive- filled nylon, known under the trade name "TYNEX") starts cutting well, but dulls rapidly to less than 5% of its original cutting ability within 1 hour under these test conditions. Comparative Example B (abrasive-filled nylon, known under the trade name "ASAHI") performed better, but not as well as the composite abrasive filaments of Examples 1-3, which started at a higher level (grams) of cut and retained their cutting abilities significantly better than the comparative Examples. This is apparent on flat 1018 CRS plate abrasion tests (FIG. 8) and perforated screen 1008 CRS abrasion tests (FIG. 9). The polyester TPE composite abrasive filaments employing TPEs with higher Shore D durometers showed more aggressive abrasive cutting action on both plate and screen. Fatigue resistance test results (Table 4) showed that abrasive-filled nylon filaments (Example A) exceeded their limits in 10-15 minutes. The softer, polyester TPE-coated composite abrasive filaments (Examples 1 and 4) remained usable greater than 2 hours, while the hardest polyester-coated composite abrasive filaments (Examples 3, 7-9) were usable only for very short times. The best balance of fatigue resistance and abrasive cut on both steel plate and screen using polyester TPE-coated composite abrasive filaments was obtained with the polyester TPE having Shore D durometer of 63. FIG. 10 shows that cutting ability of the composite abrasive filament of Example 4 (334 abrasive) is less than Example 5 (50% abrasive) on both 1018 CRS plate (+) and 1008 CRS screen (*). It appears that the composite abrasive filaments allow higher abrasive loading and hence greater amount of workpiece removed. FIGS. 11 and 12 compare the results of cutting vs. time for Examples A, 4, and 5, on both 1018 CRS plate and 1008 CRS screen, showing that the composite abrasive filaments significantly out perform the abrasive-filled nylon abrasive filament to a greater degree with higher percent abrasive loading. FIGS. 13 and 14 compare cutting performance of abrasive filaments A, C, 2 and 6 of Table 3. With abrasive-filled polyester TPE-coated, stainless steel preformed core composite abrasive filaments, aluminum oxide abrasive- containing composite abrasive filaments of the invention were more aggressive than silicon carbide abrasive-containing composite abrasive filaments on both 1018 CRS plate and 1008 CRS screen. A second set of composite filaments were prepared with fused aluminum oxide abrasive grains, heat treated aluminum oxide abrasive grains, and ceramic aluminum abrasive grains (the latter known under the trade designation "Cubitron") in Examples A, 7-9. FIGS. 15 and 16 show the results of abrasion tests on similar steel plate and screen, respectively. In Examples 7-9, glass plied yam preformed cores were coated with abrasive-filled 72 Shore D durometer polyester TPE known under the trade designation "Hytrel 7246". From experiments with abrasive-filled nylon filaments, it was not expected that there would be any significant difference in abrasive cut between aluminum oxide or silicon carbide-filled thermoplastic elastomers coated composite abrasive filaments of the invention. However, quite surprisingly, the aluminum oxide and silicon carbide abrasive- filled composite abrasive filaments gave two to four times better cut than aluminum oxide-filled nylon abrasive filaments on flat plate (compare FIGS. 13 and 15), and the heat treated aluminum oxide-filled composite abrasive filaments of the invention performed significantly better on screen (FIGS. 14, 16). FIGS. 15 and 16 show that abrasive action can be significantly increased using the composite abrasive filaments of the invention when better grades of abrasives are employed. FIGS. 17-20 present, in bar graph form, comparative abrasion tests using filament Examples D, E, and 10-13 to compare the performance of filaments employing P320 and P220 aluminum oxide and silicon carbide abrasive particles. In each of Examples 10-13 the segmented polyester TPE known under the trade name "Hytrel 6356" was coated over glass yam known under the product code "OCF G75 PY" available from Owens Corning. FIG. 17 presents test results for the filaments abrading copper plate, while FIGS. 18- 20 present test results for filaments abrading titanium, 304 stainless steel, and aluminum 6061 T6, respectively. These data show that marked differences in abrasive performance resulted when a variety of workpieces were abraded. Composite abrasive filaments employing 320 grade silicon carbide exhibited low cut whereas both grades of aluminum oxide showed much higher cut on copper. Titanium proved to be an unusual metal workpiece. Silicon carbide and aluminum oxide abrasive particles employed in the control abrasive-filled nylon filaments exhibited the greatest cut values on this metal. On 304 stainless steel workpieces, the results were remarkably different. The commercially available abrasive-filled nylon filaments were relatively ineffective, whereas composite abrasive filaments of the invention employing the same abrasive particles in the segmented polyester TPE known under the trade designation "Hytrel 6356" were much more effective. Finally, a very unexpected result was obtained when T6061 aluminum workpieces were abraded. Composite abrasive filaments containing alternately silicon carbide and aluminum oxide abrasive particles, in both 220 and 320 grades, remarkably outperformed commercially available abrasive-filled nylon filaments. FIGS. 21-22 represent, in bar graph form, the results of abrasion tests on 1018 CRS steel plate (FIG. 21) and 1008 CRS steel screen (FIG. 22), respectively, for Example composite abrasive filaments 14-16. These examples utilized P120 aluminum oxide abrasive-filled polyamide TPE coatings on glass plied yam preformed cores. FIG. 21 shows that these filaments were not as aggressive on steel plate, but were quite aggressive on steel screen (FIG. 22). FIGs. 23 and 24 are similar to FIGS. 21-22 in that Example filaments 17-22 performed well on 1008 CRS steel screen (FIG. 24) but were not as aggressive on 1018 CRS steel plate (FIG. 23). FIGS. 25-28 represent, in bar graph form, the results of abrasion testing using cylindrical bmshes (10.2 cm OD) with very dense filament packing on the hubs. Filaments E and 10-13 were compared using a printed circuit board brushing apparatus known under the trade designation "Chemcut". The cylindrical bmshes were turned at 2500 rpm against substrates of 1018 steel, 304 stainless steel, copper, and 6061 T6 aluminum (FIGS. 25-28, respectively) at different power levels as indicated. Composite abrasive filaments of the present invention performed substantially better than abrasive-filled nylon abrasive filaments on 1018 CRS steel, 304 stainless steel, and performed comparatively well on copper and T6061 aluminum.

Claims: CLAIMS: 1. A composite abrasive filament characterized by the feature that at least one preformed core is at least partially coated with a thermoplastic elastomer having abrasive particles dispersed and adhered therein, said thermoplastic elastomer and abrasive particles together comprising a hardened composition. 2. A composite abrasive filament in accordance with claim 1 further characterized by the feature that said preformed core is at least one wire or fiber materials selected from the group consisting of metal wire, glass fiber, ceramic fiber, natural fiber, organic synthetic fiber, inorganic synthetic fiber, and combinations thereof. 3. A composite abrasive filament in accordance with claim I further characterized by the feature that said thermoplastic elastomer is selected from the group consisting of segmented thermoplastic elastomers, ionomeric thermoplastic elastomers, blends of thermoplastic elastomers and thermoplastic polymers, and mixtures thereof. 4. A composite abrasive filament in accordance with claim 1, further characterized by the feature that said preformed core is a plied yam of fibers selected from the group consisting of glass fibers, ceramic fibers, natural fibers, organic synthetic fibers, inorganic synthetic fibers, and combinations thereof. 5. A composite abrasive filament in accordance with claim 3, further characterized by the feature that said thermoplastic elastomer has a Shore D durometer hardness ranging from about 30 to about 90. 6. An abrasive article including at least one composite abrasive filament, the composite abrasive filament characterized by the feature that it has at least one preformed core at least partially coated with a thermoplastic elastomer having abrasive particles dispersed and adhered therein, the thermoplastic elastomer and abrasive particles together comprising a hardened composition, with the proviso that if there is more than one composite abrasive filament, the composite abrasive filaments can be the same or different. 7. An abrasive article in accordance with claim 6, further characterized by the feature that said preformed core is at least one wire or fiber of materials selected from the group consisting of metal wire, glass fiber, ceramic fiber, natural fiber, synthetic fiber, and combinations thereof. 8. An abrasive article in accordance with claim 6 further characterized by the feature that said thermoplastic elastomer is selected from the group consisting of segmented thermoplastic elastomers, ionomeric thermoplastic elastomers, blends of thermoplastic elastomers and thermoplastic polymers, and mixtures thereof. 9. A method of making a composite abrasive filament, the composite abrasive filament including at least one preformed core at least partially coated with a thermoplastic elastomer having abrasive particles dispersed and adhered therein, the thermoplastic elastomer and abrasive particles together comprising a hardened composition, said method characterized by the steps of: (a) rendering a thermoplastic elastomer molten and combining abrasive particles therewith; (b) coating at least a portion of a preformed core with a coating comprising the molten thermoplastic elastomer and abrasive particles; and (c) cooling the coating to a temperature sufficient to harden the molten thermoplastic elastomer and thus form the hardened composition. 10. A method in accordance with claim 9, further characterized by the feature that step (a) comprises passing the preformed core and molten thermoplastic elastomer simultaneously through a die.

Inventors: BARBER LOREN L JR, PIHL RICHARD M, WELYGAN DENNIS G, BARBER, LOREN, L., JR., PIHL, RICHARD, M., WELYGAN, DENNIS, G.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1993
Main classification: D01F8
IPC codes: A46D1, B24D3, B24D13, B29C47, B29C70, D01D5, D01F1, D01F8, D02G3, D06M15, D06M101