DUAL DUROMETER HANDLES

Abstract: A dual durometer thermoplastic polyurethane or thermoplastic polyurethane-containing handle suitable for human grip provides mechanical strength and chemical resistance and can be prepared without the use of adhesives.

Description: DUAL DUROMETER HANDLES This invention relates to a dual durometer thermoplastic polyurethane handle made from rigid and soft thermoplastic polyurethanes. Hand grips for tools or sporting equipment which provide comfort to the user are known in the art. For example, Uke et al. in U.S. Patent No. 4,953,862 describes a sleeve of a semisolid or stiff elastomeric material. Smith in U.S. Patent No.4,452,862 describes a handle made from rubber encapsulating a relatively hard plastic core. Coyle in U.S. Patent No. 2,871 ,899 describes a tool handle made from a soft plastic sleeve surrounding a rigid material. Kusznir in U.S. Patent No. 4,721,021 describes a handle made of a strong durable elastic material and a soft engaging foamed synthetic rubber pad extending longitudinally from the handle. The pad is pressed into engagement with the durable elastic material. It would be an advance in the art to provide a dual durometer handle with both mechanical strength and chemical resistance that can be prepared without the use of adhesives. The present invention is a dual durometer thermoplastic polyurethane handle suitable for grip by a human hand, comprising: a) a rigid thermoplastic polyurethane core having a glass transition temperature above 50°C, or a thermoplastic polyurethane-containing core having a flex modulus of at least 100,000 psi; and b) a soft thermoplastic polyurethane material having a glass transition temperature below 25°C, or a thermoplastic polyurethane blend having a Shore A hardness not greater than 95, the soft polyurethane material or thermoplastic polyurethane blend superposing at least a portion of the rigid thermoplastic polyurethane or the thermoplastic polyurethane-containing material of (a) so that a hand, upon gripping the handle, contacts the soft thermoplastic polyurethane material. The handle of the present invention can be made without the use of an adhesive. The handle provides comfort, strength, and chemical resistance. Figure 1 is a side view of a dual durometer screwdriver having a handle made with the thermoplastic polyurethanes of the present invention. Figure 2 is a cross-sectional view of the dual durameter handle taken on line 2-2 of Figure 1. Figure 3 is a side view of a dual durometer screwdriver handle showing a sheath of a soft polyurethane material covering a core of a rigid thermoplastic polyurethane. The tool chosen for illustration of a preferred embodiment of the present invention is a screwdriver. It is to be understood that a screwdriver handle is merely illustrative and not meant to restrict the scope of the application. Figure 1 shows a screwdriver 10 having an elongated rigid thermoplastic polyurethane core 12 having a proximal end 16 and a distil end 18. The core 12 has a plurality of longitudinally extending grooves filled with soft thermoplastic polyurethane grip strips 14. The grip strips 14 protrude above the surface of the core 12 so that a human hand would grip the grip strips 14. The distil end 18 of the core 12 has a shank-receiving recess extending inwardly from the distil end to receive a tool bit 20. The core may be a rigid thermoplastic polyurethane material (RTPU) or any thermoplastic polyurethane-containing material having a flex modulus of at least 100,000 psi. The term RTPU refers to a thermoplastic polyurethane (TPU) having a T g of at least 50°C. The RTPU has a hard segment that preferably constitutes from 75, more preferably from 90, to 100 weight percent based on the total weight of the RTPU; and a soft segment that preferably constitutes from 0 to 25, more preferably to 10 weight percent based on the total weight of the RTPU. A TPU that is not by definition an RTPU may be used as the core of the handle of the present invention provided sufficient amounts of suitable fillers, reinforcing fibers, or other thermoplastic materials are added to achieve the desired core flex modulus. Suitable fillers include talc, silica, mica, or glass beads, or mixtures thereof; suitable reinforcing fibers include glass, carbon, or graphite fibers, or mixtures thereof; and suitable thermoplastics include acrylonitrile-butadiene-styrene, polyacetal, nylon, polybutylene terephthalate, polyethylene terephthalate and ionomers. The core is superposed by a soft thermoplastic polyurethane (STPU) or any TPU blend having a Shore A hardness of not more than 95. The STPU has a T g of not more than 25°C. Preferably, the STPU has a hard segment of 15, more preferably 20, and most preferably 25, to 50, more preferably 40, and most preferably 30 weight percent based on the total weight of the STPU. Preferably, the STPU has a soft segment of 50, more preferably 60, and most preferably 70, to 85, more preferably 80, and most preferably 75 weight percent based on the total weight of the soft TPU. Examples of materials used to create a TPU blend having a Shore A hardness of not more than 95 include natural butyl rubber, styrene-isoprene-styrene and styrene- butadiene-styrene triblock copolymers, and polyolefinic materials containing maleic anhydride grafts. The amounts of such materials used will, of course, vary depending on the material and the hardness desired. The hard segment of the TPUs is a block derived from the reaction between a polyisocyanate and a difunctional chain extender. Preferred polyisocyanates include aromatic, aliphatic, and cycloaliphatic diisocyanates and combinations thereof. Representative examples of these preferred diisocyanates can be found, for example, in U.S. Patent Nos. 4,385,133; 4,522,975; and 5,167,899. More preferred diisocyanates include 4,4'-diisocyanatodiphenylmethane, p-phenylene diisocyanate, 1 ,3-bis(isocyanatomethyl)cyclohexane, 1 ,4-diisocyanatocyclohexane, hexamethylenediisocyanate, 1 ,5-naphthalenediisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, 4,4'-diisocyanatodicyclohexylmethane, and 2,4-toluenediisocyanate, or mixtures thereof. More preferred is 4,4'-diisocyanatodicyclohexylmethane and 4,4'-diisocyanatodiphenylmethane. Most preferred is 4,4'-diisocyanatodiphenylmethane. The difunctional chain extender is a polyol having a molecular weight of not greater than 200. Preferred chain extenders are ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, tetraethylene glycol, neopental glycol, 1 ,4-cyclohexanedimethanol, 1,4-bis-hydroxyethylhydroquinone, and mixtures thereof. More preferred chain extenders are 1,4-butanediol, 1,6-hexanediol, and 1,4-cyclohexanedimethanol, and mixtures thereof. The soft segment of the TPUs is derived from a polyol which has a molecular weight in the range preferably from 500, more preferably from 1000, most preferably from 1500, to preferably 6000, more preferably to 4000, and most preferably to 3000. The polyol is preferably a polyester polyol or a polyether polyol or combinations thereof. Examples of preferred polyester polyols and polyether polyols include polycaprolactone glycol, polyoxyethylene glycol, polyoxypropylene glycol, polyoxyethylene/polyoxypropylene glycol copolymer, polyoxytetramethylene glycol, polyethylene adipate, polybutylene adipate, polyethylene-butylene adipate, and poly(hexamethylene) carbonate glycol, or combinations thereof. In a preferred embodiment, the handle comprises an RTPU core superposed by an STPU. The RTPU core is preferably an ISOPLAST™ engineering thermoplastic resin (trademark of The Dow Chemical Company) and the STPU is preferably a PELLETHANE'" polyurethane elastomer (trademark of The Dow Chemical Company) having a Shore A durometer hardness of 90 or less. Preferably, the PELLETHANE™ polyurethane elastomer has a Shore A durometer hardness of 80 or less, more preferably 75 or less. The handle of the present invention can be transparent or opaque but is preferably transparent. The shape of the handle is not critical, though it is preferably elongated. The handle can be produced by a variety of techniques, including coextrusion, coinjection, and two-shot overmolding. In the coextrusion technique, for example, a primary extruder extrudes the grooved rigid thermoplastic polyurethane core while a second extruder extrudes the soft thermoplastic polyurethane through a crosshead die into the grooves of the rigid core. The distribution and the amount of STPU superposing the core is not critical so long as the user feels the STPU when gripping the handle. The core is preferably grooved, and the superposed material is preferably contained in and protruding from the grooves of the core. The configuration of the dual durometer handle may be that of an inner core surrounded by a sheath of STPU or soft TPU-containing material. This embodiment may be produced through a two-shot overmolding process, for example. Whichever process is used, the core and the superposing material adhere to each other without glue, solvent, or any other adhesive. Though not bound by theory, it is believed that covalent bonds form across the STPU-RTPU interface through depolymerization and repolymerization during the processing of the handle, wherein freed hydroxyl groups from one of the TPUs react with freed isocyanate groups from the other of the TPUs. It is also possible that adhesion takes place through diffusion of polymer chains across the RTPU-STPU interface. The handle can be any kind of handle that is suitable for human grip. Examples include, but are not restricted to, handles for sports equipment, such as baseball bats, racquets, golf clubs, and waterski tow lines; handles for household items, such as refrigerator doors, oven doors, hand mixers, and door knobs; and hand tools, such as handles for hammers, saws, power drills, torque wrenches, and, of course, screw drivers.

Claims: CLAIMS 1. A dual durometer thermoplastic polyurethane handle suitable for grip by a human hand, comprising: a) a rigid thermoplastic polyurethane core having a glass transition temperature above 50°C, or a thermoplastic polyurethane-containing core having a flex modulus of at least 100,000 psi; and b) a soft thermoplastic polyurethane material having a glass transition temperature below 25°C, or a thermoplastic polyurethane blend having a Shore A hardness not greater than 95, the soft polyurethane material or thermoplastic polyurethane blend superposing at least a portion of the rigid thermoplastic polyurethane or the thermoplastic polyurethane-containing material of (a) so that a hand, upon gripping the handle, contacts the soft thermoplastic polyurethane material. 2. The handle of Claim 1 comprising a soft thermoplastic polyurethane material having a glass transition temperature below 25°C superposing a rigid thermoplastic polyurethane core having a glass transition temperature above 50 C C. 3. The handle of Claim 1 wherein the rigid thermoplastic core is elongated and has a plurality of longitudinally extending grooves wherein the soft thermoplastic material is contained, such that the soft thermoplastic material protrudes above the surface of the rigid thermoplastic polyurethane core. 4. The handle of Claim 3 wherein from 75 to 100 weight percent of the rigid thermoplastic polyurethane core contains hard segments derived from a diisocyanate selected from 4,4'-diisocyanatodiphenylmethane, p-phenylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-diisocyanatocyclohexane, hexamethylenediisocyanate, 1,5-naphthalenediisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, 4,4'-diisocyanatodicyclohexylmethane, or 2,4-toluenediisocyanate. 5. The handle of Claim 4 wherein from 15 to 40 weight percent of the soft thermoplastic polyurethane material contains hard segments derived from a diisocyanate selected from 4,4'-diisocyanatodiphenylmethane, p-phenylene diisocyanate, 1 ,3-bis(isocyanatomethyl)cyclohexane, 1 ,4-diisocyanatocyclohexane, hexamethylenediisocyanate, 1,5-naphthalenediisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, 4,4'-diisocyanatodicyclohexylmethane, or 2,4-toluenediisocyanate. 6. The handle of Claim 5 wherein at least from 90 to 100 weight percent of the rigid thermoplastic polyurethane core and from 10 to 25 weight percent of the soft thermoplastic polyurethane material comprises moieties derived from a diisocyanate selected from 4,4'-diisocyanatodiphenylmethane and 4,4'-diisocyanatodicyclohexylmethane. 7. The handle of Claim 6 wherein the rigid thermoplastic polyurethane core is prepared by the reaction of 4,4'-diisocyanatodiphenylmethane and a diol selected from 1,6-hexanediol, 1,4-butanediol, or 1,4-cyclohexanedimethanol. 8. The handle of Claim 7 wherein the soft thermoplastic polyurethane is prepared by the reaction of 4,4'-diisocyanatodiphenylmethane; a diol selected from 1,4-butanediol, 1,6-hexanediol or 1,4-cyclohexanedimethanol; and a polyol having a molecular weight in the range of 1000 to 2000 and selected from polycaprolactonediol glycol, polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol, polyethylene adipate, polybutylene adipate, polyethylene-butylene adipate, or poly(hexamethylene) carbonate glycol. 9. A dual durometer thermoplastic polyurethane handle suitable for grip by a human hand, comprising an ISOPLAST * " engineering thermoplastic core superposed by a PELLETHANE'" polyurethane elastomer. 10. The handle of Claim 9 wherein the ISOPLAST'" engineering thermoplastic polyurethane core is elongated and has a plurality of longitudinally extending grooves wherein the PELLETHANE'" polyurethane elastomer is contained, such that the PELLETHANE'" polyurethane elastomer protrudes above the surface of the ISOPLAST'" engineering thermoplastic core. AMENDED CLAIMS [received by the International Bureau on 23 April 1996 (23.04.96); original claims 9 and 10 cancelled; remaining claims unchanged (1 page)] 7. The handle of Claim 6 wherein the rigid thermoplastic polyurethane core is prepared by the reaction of 4,4'-diisocyanatodiphenylmethane and a diol selected from 1,6-hexanediol, 1,4-butanediol, or 1,4-cyclohexanedimethanol. 8. The handle of Claim 7 wherein the soft thermoplastic polyurethane is prepared by the reaction of 4,4'-diisocyanatodiphenylmethane; a diol selected from 1 ,4-butanediol, 1 ,6-hexanediol or 1,4-cyclohexanedimethanol; and a polyol having a molecular weight in the range of 1000 to 2000 and selected from polycaprolactonediol glycol, polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol, polyethylene adipate, polybutylene adipate, polyethylene-butylene adipate, or poly(hexamethylene) carbonate glycol. 9. Cancelled. 10. Cancelled.

Inventors: MOSES PAUL J JR, OERTEL RICHARD W III, REMMERT MARK A, MOSES, PAUL, J., JR., OERTEL, RICHARD, W., III, REMMERT, MARK, A.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1995
Main classification: B25G1
IPC codes: B25G1, B29D31, B32B27, B32B37, C08L75