Hybrid golf club shaft

FIELD OF THE INVENTION

This invention relates generally to golf clubs and, more particularly, to a hybrid shaft for improving the performance of golf clubs.

BACKGROUND OF THE INVENTION

A modern golf club typically comprises a shaft, a head connected to the shaft's tip end, and a grip disposed at the shaft's butt end. Perhaps more than any other component, the shaft affects overall club performance. It is generally accepted that the optimal golf club shaft should have lightweight, high torsional stiffness, configurable bending stiffness, and provide moderately high swing weight and vibration-damping property.

A lightweight club generates greater acceleration, which in turn yields a higher swing velocity, than a heavy club does for the same amount of applied force. For clubs of similar weight and mass distribution, the greater the swing velocity, the farther the ball will travel when driven by the clubs. Torsional stiffness is preferred to limit unwanted angular deflection of the head about the shaft. This allows the face of the club head to impact the ball squarely so that the ball's flight will follow a straight path. The torsional stiffness may be enhanced by enlarging the shaft's diameter to increase polar moment of inertia, as well as by using materials having high Young's modulus such as steel.

Skilled golfers who generate high swing velocity prefer clubs having a high bending stiffness. Average golfers, on the other hand, like clubs with low bending stiffness to take advantage of the “kick” resulting from shaft flexing during early part of swing and subsequent release as the golf club head impacts the ball. But golfers of all levels want a set of clubs having essentially the same swing weights to achieve consistent play. Swing weight is a measure of how the mass is distributed on a club and equates to the dynamic characteristics or “feel” of the club. Tip-weighted shafts and/or heavy club heads tend to increase the clubs' swing weights, while butt-weighted shafts and/or light club heads tend to decrease the clubs' swing weights. A desirable club should also incorporate vibration-damping materials to absorb tactile shock and reduce acoustic propagation caused by the head striking the ball and/or ground.

There are essentially three existing club shaft designs, including metal shafts, composite shafts, and hybrid shaft of metal and composite material. Conventional shafts often optimize some of the characteristics mentioned above while compromising others.

The metal shaft, typically formed from steel, has long been the mainstay of golf club design. Steel has a high shear modulus, giving the shafts an inherently high torsional stiffness. Shafts of various bending stiffness and swing weights can be obtained by manipulating the thickness and lengths of the flexible tip portion and the rigid butt portion. Steel is also durable, strong, inexpensive, and provides great consistency of characteristics from one shaft to another. Unfortunately, steel is dense, and clubs having steel shafts are heavy, have relatively poor acceleration and consequently a lower swing velocity. Additionally, The conventional heavy rubber grip used with the steel shaft, comprising about 15% or more of the total mass of a typical driver or any fairway woods, further compounds the weight and weight distribution problems. Steel shafts are also very poor in absorbing shocks or damping vibrations.

Club shafts comprising composite materials such as graphite are commonly preferred over steel shafts because they can be made extremely lightweight and conform to desired flexural characteristics. The light graphite shaft affords the club with high swing velocity, which produces long drives. Primary drawbacks of the composite graphite designs are their high bending stiffness and low torsional stiffness. To provide a composite shaft with the same torsional stiffness as a metal shaft, particularly in the tip end where the torsional stress is great, many plies of high modulus fibers oriented at ±45 degree angle to the longitudinal axis of the shaft must be incorporated. Unfortunately, these fibers add significant bulk and weight in a particularly undesirable location on the shaft. Additionally, graphite composite shafts are more likely to break, particularly at the tip portion, the part of the shaft with the smallest diameter. Nonetheless, most golfers prefer composite shafts because they are lightweight and have a more pleasant “feel” at impact than steel shafts. Composite shafts are also less sensitive to resonance phenomena since graphite composites are good vibration damping materials.

Hybrid shaft designs typically incorporate both metal and composite materials. U.S. Pat. Nos. 4,836,545 and 5,253,867 both disclose two-piece hybrid shafts that join together a lower metal tip portion with an upper composite butt portion. U.S. Pat. No. 5,028,464 discloses a golf club shaft having a laminated composite tube on the inside, a resin coat on the outside, and a transparent metallic layer disposed between the laminated tube and the resin coat. The transparent metallic layer is formed by depositing or plating a very thin layer of a metallic element onto a transparent cloth of organic and/or organic fibers impregnated with a thermosetting or thermoplastic resin. U.S. Pat. No. 5,083,780 discloses a tubular metal shaft having a short shell of reinforced composite molded over a predetermined location on the metal shaft to control the bending point of the shaft. U.S. Pat. No. 5,259,614 discloses a golf club shaft having a hollow steel tubular core and a composite filament spirally wound about the core to form a seamless jacket thereabout. U.S. Pat. No. 5,607,364 discloses a golf club shaft including a damping layer coated to the inner diameter of the shaft, and the damping layer is formed from a viscoelastic material. U.S. Pat. No. 5,904,628 discloses, among others, a lightweight hollow metal golf club shaft with an inflatable and flexible bladder which is pressurized by a gas to rigidify, reinforce and enhance the performance of the shaft. U.S. Pat. No. 6,139,444 discloses a hollow composite shaft having a preformed sheath metal tube surround the tip portion of the composite shaft as an external stiffener. U.S. Pat. No. 6,302,806 discloses a composite shaft having steel filaments aligned longitudinally in the tip portion for weighting, and steel filaments aligned longitudinally in the butt portion for reinforcement, thereby adjusting center of gravity and bending point of the shaft. U.S. patent application Ser. No. 09/248,569 discloses a hybrid shaft having a steel tip portion and a composite butt portion joined together, and the steel tip has a vibration damping member embedded therein. U.S. patent application Ser. No. 09/813,608 discloses a steel golf shaft having a steel tip portion and a steel butt portion joined by a composite pivot portion via connectors of various configurations.

There remains a need, however, for an improved golf club shaft that is light weight and provides the improved feel and vibration damping of fiber/resin composite shafts, as well as increased torsional stiffness and resistance to breakage of metal shafts.

SUMMARY OF THE INVENTION

The present invention is directed to a hollow golf club shaft of circular cross section having a tubular cover layer and a tubular core layer. The cover layer and the core layer are conjoined and coextend substantially the entire length of the shaft. Preferably, the cover layer has a thickness of less than about 0.2 inches, and the core layer has a thickness of less than about 0.3 inches. The cover layer is formed from an isotropic material such as metal matrix composites, metals and alloys thereof, including titanium, steel, stainless steel, aluminum, tungsten, nickel, copper, zinc, brass, bronze, magnesium, tin, gold, or silver. Preferably, the cover layer is a solid, continuous and non-porous metallic sheath.

The core layer is formed from a non-isotropic material, such as a reinforcement material, preferably impregnated with a vibration damping thermosetting or thermoplastic resin. Suitable reinforcement material include carbon fibers, graphite fibers, glass fibers, quartz fibers, boron fibers, ceramic fibers, ceramic whiskers, metal-coated fibers, ceramic-coated fibers, diamond-coated fibers, carbon nanotubes, extended-chain polyethylenes, poly-p-phenylenebenzobisoxazole fibers, metal fibers, polythenes, polyarylates, polyacetals, liquid crystalline polymers, aromatic polyesters, or polyallylates. Suitable resins include epoxy, polyester, polystyrene, polyurethane, polyurea, polycarbonate, polyamide, polyimide, polyethylene, polypropylene, polyether, polyvinyl halide, polyvinylidene halide, nylon, nylon 6, polyphenylene sulfide, polyether ether ketone, polyether ketone ketone, polyamide imide, polyether imide, polyaryl sulfone, polyether sulfone, or liquid crystal polymer. Preferably, substantially all of the reinforcement material is aligned longitudinally along the shaft. The thermosetting or thermoplastic resin has a loss factor of between about 0.2 and about 1.2 at 100 Hz and 68° F., a shear storage modulus of at least about 1,000 psi, and a Young's modulus of at least about 0.01 Mpsi. In one embodiment, the non-isotropic material is epoxy-impregnated carbon or graphite fibers, and the carbon or graphite fibers are present in an amount of from about 10% to about 80% by volume of the non-isotropic material.

Preferably, the shaft has a total weight of less than about 130 grams, the cover layer has a weight of less than about 80 grams, and the core layer has a weight of less than about 100 grams. The shaft may further have a vibration damping layer formed of at least one viscoelastic material disposed between the core layer and the cover layer, wherein the vibration damping layer comprises. Preferably, the viscoelastic material has a Young's modulus of at least about 15 psi, a shear storage modulus of at least about 10 psi, a strain energy ratio of at least about 2%, and a loss factor of at least about 0.01 at a temperature range of −40° C. to 100° C. and a frequency range of 1 Hz to 10,000 Hz. More preferably, the vibration damping thermosetting or thermoplastic resin in the core layer is substantially the same as the viscoelastic material. The vibration damping layer preferably has a thickness of less than about 0.1 inches, covers at least about 5% of the shaft length, and can be a continuous layer, a discontinuous layer, a layer of uniformed thickness, a layer of non-uniformed thickness, a lattice network layer, a wound layer, a woven layer, a braided layer, or a laminar layer. The shaft may further comprises a reinforcing layer embedded in or disposed on an inner surface of the core layer, having a length of at least about 5% of the shaft length.

The invention is also directed to a hollow golf club shaft of circular cross section comprised of a tubular cover layer formed from an isotropic material having a Young's modulus of at least about 5 Mpsi, and a tubular core layer formed from a non-isotropic material. Preferably, the cover layer and the core layer are conjoined and coextend substantially the entire length of the shaft. The non-isotropic material of the core layer includes a reinforcement material and a thermosetting or thermoplastic resin. The resin preferably has a Young's modulus less than the isotropic material of the cover layer by at least about one order of magnitude. The cover layer has a thickness ranging from about 0.001 inches to about 0.15 inches, and the core layer has a thickness ranging from about 0.001 inches to about 0.2 inches. The shaft may further include a vibration damping layer between the cover layer and the core layer having a thickness ranging from about 0.0005 inches to about 0.05 inches, and/or a reinforcing layer embedded in or disposed on an inner surface of the core layer having a thickness of less than about 0.1 inches.

The invention is further directed to a hollow golf club shaft of circular cross section having a tubular cover layer formed from an isotropic material and a tubular core layer formed from a non-isotropic material, wherein the cover layer and the core layer are conjoined and coextend substantially the entire length of the shaft, and a volume ratio of the core layer to the cover layer is less than about 20:1. Any one location along the shaft preferably has a thickness ratio of the cover layer to the core layer ranging from about 5:95 to about 90:10. The outer surface of the core layer can be conjoined to the inner surface of the cover layer through structural adhesives, contact adhesion, physical bonding, or chemical bonding. Preferably, the structural adhesives is one-part heat-cured epoxies, two-part reaction-cured epoxies, two-part reaction-cured polyurethanes, acrylics, double-coated bonding tapes, pressure-sensitive adhesives, or heat-cured epoxy/acrylic hybrid adhesives.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a perspective view of a golf club having a multi-layer shaft in accordance with the present invention;

FIG. 2

is a perspective view of another golf club having an alternative multi-layer shaft in accordance with the present invention;

FIG. 3

is a longitudinal sectional view of the multi-layer golf shaft of

FIG. 1

;

FIG. 4

is a longitudinal sectional view of the multi-layer golf shaft of

FIG. 2

;

FIGS. 5-10

are cross-sectional views of multi-layer golf shafts according to the present invention;

FIGS. 11 and 12

are longitudinal sectional views of a bladder mold for the production of a multi-layer golf shaft; and

FIGS. 13 and 14

are longitudinal sectional view of another bladder mold for the production of an alternative multi-layer golf shaft.

DEFINITIONS

As used herein, the term “Young's modulus,” also known as “elastic modulus” and “tensile modulus,” is a measurement of a material's stiffness and is defined as the ratio of stress to strain Young's modulus can be used to predict the elongation or compression of an object as long as the stress is less than the yield strength of the material.

As used herein, the term “isotropic” refers to a material with properties such as stiffness that remain the same independent of the loading direction or the plane on which the load is applied. Such materials have only 2 independent variables (i.e. elastic constants) in their stiffness and compliance matrices. The two elastic constants are usually expressed as the Young's modulus E and the Poisson's ratio v. However, alternative elastic constants K (bulk modulus) and/or G (shear modulus) can also be used.

Intuitively, the term “non-isotropic” used herein refers to a material that is not isotropic. A non-isotropic material may be “anisotropic,” which denotes a material having certain properties that are different in different directions, or “quasi-isotropic,” which refers to a condition wherein properties are nearly identical in all directions. Particularly in fiber-reinforced composites, quasi-isotropic condition can be attained by providing at least three directions with reinforcement in similar layer thickness.

As used herein, the term “loss factor” represents a measure of the energy dissipation of the vibration damping material and depends on the frequency and temperature experienced by the material.

As used herein, the term “shear storage modulus,” also known as “storage modulus,” is denoted as G′ and refers to the ratio of shear stress to strain (deformation) when dynamic (sinusoidal) deformation is applied in a cone-and-plate rheometer. It relates to the elastic energy stored in a viscoelastic material and released periodically. Loss modulus, G″, also determined in dynamic (sinusoidal) measurements, relates to the material's viscous behavior. G′ and G″ together give an idea of the dual nature of the viscoelastic material (partly elastic solid and partly viscous fluid). Measurements of G′ and G″ provide information on polymer structure and might be related to molecular weight distribution, cross-linking, etc.

As used herein, the term “strain energy ratio” refers to the ratio of elastic strain energy in a viscoelastic material to the total strain energy in the material.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures, a discussion of the above features with respect to preferred embodiments is provided below. It should be understood that such embodiments are for illustrative purposes, and should not be construed as limiting the scope of the invention.

FIG. 1

shows a golf club

10

that comprises a tubular multi-layer shaft

12

of the present invention. The shaft

12

substantially tapers downward through its entire length from an upper (larger diameter) butt portion

14

to a lower (smaller diameter) tip portion

16

. A club head

18

is attached to the end of the tip portion

16

, and an optional grip

19

is attached to the butt portion

14

. The tip portion

16

(typically less than about ⅓ the entire length of the shaft

12

) and/or the butt portion

14

(typically less than about ⅓ the entire length of the shaft

12

) can be tapered or parallel.

An alternative multi-layer shaft

20

, as depicted in

FIG. 2

, has a stepped-down shaft

20

with the club head

18

attached to its tip portion

16

and the optional grip

19

attached to its butt portion

14

. The shaft

22

is assembled from a plurality of tubular portions

24

having decreasing diameters. Each of the tubular portions

24

can independently be either substantially tapered or substantially parallel. Of course, the present invention is also applicable to shafts that are substantially parallel throughout their entire lengths. That is, butt portion

14

and tip portion

16

and any portion therebetween have about the same outer diameter. The butt portion

14

has an outer diameter of between about 0.5 inches and about 0.9 inches, while the tip portion

16

has an outer diameter of between about 0.2 inches and about 0.6 inches. The shafts

12

and

22

typically have a length of about 30 inches to about 65 inches.

FIGS. 3 and 4

illustrate the longitudinal sectional views of shafts

12

and

22

in

FIGS. 1 and 2

, respectively. Shaft

12

has a tubular cover layer

30

and a tubular core layer

32

, both coextensive substantially the entire length of the shaft

12

. Similarly, shaft

22

also includes cover layer

30

and core layer

32

. For simplicity reasons, the following descriptions use shaft

12

as the example. A person of ordinary skill in the art can readily apply the same compositions, dimensions, and configurations for shaft

12

in the production of shaft

22

.

Referring to

FIG. 3

, cover layer

30

may be a continuous layer formed from at least one isotropic material having a Young's modulus of preferably greater than about 5 Mpsi, and more preferably greater than about 10 Mpsi. The isotropic material may be a metallic material such as metal matrix composites, metals, or alloys thereof including one or more combinations of metallic constituents. Among the numerous metals that are suitable for cover layer

30

, ferrous metals such as titanium, steel, stainless steel, aluminum and tungsten are particularly useful. Additionally, certain non-ferrous metals including nickel, copper, zinc, brass, bronze, magnesium, tin, gold and silver may be employed generally as alloying agents. Metal matrix composites that are quasi-isotropic may also be desirable for use in cover layer

30

. Preferably, cover layer

30

is a single solid, continuous and non-porous metallic sheath of steel, titanium, or an alloy thereof.

Core layer

32

is formed from a non-isotropic (i.e. either anisotropic or quasi-isotropic) material, preferably having a reinforcement material. The reinforcement material may be in the forms of particles, flakes, whiskers, continuous or discontinuous fibers, filaments, ribbons, sheets, and the like or mixtures thereof. Suitable reinforcement material includes carbon fibers, graphite fibers, glass fibers, quartz fibers, boron fibers, ceramic fibers or whiskers such as alumina and silica, metal-coated fibers, ceramic-coated fibers, diamond-coated fibers, carbon nanotubes, aramid fibers such as Kevlar® from DuPont, extended-chain polyethylenes such as Spectra® from Honeywell, poly-p-phenylenebenzobisoxazole (“PBO”) fibers such as Zylon® from Toyobo, metal fibers, polythenes, polyarylates, polyacetals, liquid crystalline polymers, aromatic polyesters such as Vectran® from Celanese, polyallylates, other high performance fibers, and combinations thereof. Metal-coated fibers may be any of the above fibers coated with a metal such as titanium, nickel, copper, cobalt, gold, silver, lead, etc. The reinforcement material is impregnated with thermosetting or thermoplastic resins, serving as the matrix binder and providing vibration damping effect to shaft

12

. Suitable resins include epoxy; polyester; polystyrene; polyurethane; polyurea; polycarbonate; polyamide; polyimide; polyethylene; polypropylene; polyether; polyvinyl halide; polyvinylidene halide; nylon, nylon 6, polyphenylene sulfide (“PPS”), polyether ether ketone, polyether ketone ketone, polyamide imide, polyether imide, polyaryl sulfone, polyether sulfone, liquid crystal polymer, and the like or mixtures thereof. As is well known in the art, these resins may further include modifying agents such as hardeners, catalysts, fillers, crosslinkers, and the like. Preferably, the reinforcement materials is present in core layer

32

at a volume percentage of from about 10% to about 80%, and at a weight percentage of from about 5% to about 90%. More preferably, the volume percentage is from about 30% to about 70%, and the weight percentage is from about 20% to about 75%. In the preferred embodiment, core layer

32

is formed from epoxy-impregnated carbon or graphite fibers. Commercial sources of resin pre-impregnated carbon or graphite fibers are well known in the industry.

Thickness of shaft

12

depend on specific characteristics desirable from the shaft, as well as the particular club head

18

used, and may vary from one portion of the shaft to another, but should be in a range of between about 0.01 inches and about 0.5 inches. In one embodiment, cover layer

30

preferably has a thickness of less than about 0.2 inches, more preferably from about 0.001 inches to about 0.15 inches, and most preferably from about 0.01 inches to about 0.12 inches. Core layer

32

should have a thickness of less than about 0.3 inches, preferably less than about 0.25 inches, more preferably from about 0.001 inches to about 0.2 inches, and most preferably from about 0.01 inches to about 0.18 inches. In another embodiment, a volume ratio of core layer

32

to cover layer

30

is preferably less than about 20:1, more preferably less than about 15:1, and most preferably less than about 10:1. Furthermore, the thickness of each layer may be non-uniformed and vary depending upon the location along the shaft. For example, cover layer

30

and/or core layer

32

may be thicker at the butt portion

14

and/or thinner at the tip portion

16

. In general, at any point along the shaft, a ratio of wall thickness between cover layer

30

and core layer

32

ranges from about 5:95 to about 90:10, more preferably from about 10:90 to about 70:30, and most preferably from about 20:80 to about 50:50. Weight of cover layer

30

is preferably less than about 80 grams, more preferably from about 1 gram to about 60 grams, and most preferably from about 10 grams to about 50 grams. Weight of core layer

32

is preferably less than about 100 grams, more preferably from about 1 gram to about 80 grams, and most preferably from about 10 grams to about 70 grams. Overall weight of shaft

12

is preferably less than about 130 grams, more preferably less than about 110 grams, and most preferably less than about 95 grams.

Advantageously, the isotropic material of cover layer

30

increases the shaft torque resistance (i.e. torsional stiffness). Cover layer

30

reinforces shaft

12

, particularly the tip portion

16

, to prevent club head

18

from twisting around the shaft's longitudinal axis during impact, thereby keeping the ball flight straight. Cover layer

30

also improves shaft

12

in its resistances to breakage at the tip portion

16

and to abrasion and weathering, as well as improves esthetic appearance of the shaft

12

, and facilitates the coupling between shaft

12

and club head

18

. The non-isotropic composite material of core layer

32

reduces the overall weight of the shaft

12

, and enhances its bending and flexion characteristics. In the preferred embodiment, substantially all of the reinforcement materials such as carbon or graphite fibers within core layer

32

are aligned at about 0° with respect to the shaft axis (i.e., longitudinally along the shaft, or parallel to the length of the shaft), so that the longitudinal stiffness of core layer

32

is greater than its transverse stiffness. With this configuration, core layer

32

controls majority of the flexural stiffness (i.e. bending resistance) of the shaft

12

. Bending stiffness ranging from L to X can be achieved simply by incrementally incorporating 0° fibers in the core layer

32

. Preferably, cover layer

30

and/or core layer

32

extend the entire tip portion

16

and middle portion of the shaft

12

, and more preferably extend substantially the entire length of the shaft

12

. In an alternative embodiment, between about 5 weight percent and about 90 weight percent of the reinforcement material may be aligned preferably at an angle of from about 10° to about 170° with respect to the shaft axis. More preferably, the alignment angle is from about 30° to about 150°, and most preferably, from about 45° to about 135°. In another embodiment, alternating layers of fiber-reinforced composite material having fiber alignment angles of about 45°, 0° and 135° are stacked together to form core layer

32

. Preferably the amount of 45° fibers and the amount of 135° fibers are substantially the same. Optionally certain portions of the shaft

12

may be further strengthened by fiber-reinforced composite material having a fiber alignment angle of about 90°.

By virtue of its material composition, core layer

32

can reduce vibration transmission along the shaft

12

, diminish acoustic noise generation upon impact between the club head

18

and the ball, and improve the feel of the club

10

. The thermosetting or thermoplastic resins of core layer

32

as described above provide a certain level of vibration damping to the shaft

12

. Preferably, the thermosetting or thermoplastic resin of core layer

32

has a loss factor of from about 0.2 to about 1.2 at 100 Hz and 68° F., a shear storage modulus of at least about 1,000 psi, and a Young's modulus of at least about 0.01 Mpsi. The Young's modulus of the isotropic material of cover layer

30

should be at least about one order of magnitude greater than that of resin in core layer

32

. Core layer

32

may be formed by any conventional methods used to manufacture composite (graphite) shafts, including sheet or ply rolling, filament winding, multiaxial braiding, ply stacking and rolling, etc. These and other methods appropriate for the fabrication of core layer

32

are well known to one of ordinary skill in the art.

FIGS. 5-8

illustrate the cross-sections of different embodiments of the golf club shaft

12

of the present invention.

FIG. 5

depicts the basic dual-layer design having cover layer

30

encircling core layer

32

. Shown in

FIG. 6

, an optional vibration damping layer

34

comprising a viscoelastic material is disposed between cover layer

30

and core layer

32

. The viscoelastic material is capable of dissipating vibration energy by converting it into heat. Preferably, the viscoelastic material has a shear storage modulus of at least about 10 psi and a loss factor of at least about 0.01 at a temperature range of −40° C. to 100° C. and a frequency range of 1 Hz to 10,000 Hz. The viscoelastic material preferably has a Young's modulus of at least about 15 psi, and is less than that of the isotropic material of cover layer

30

by at least about one order of magnitude, preferably by at least about three orders of magnitude. Also preferred, the viscoelastic material has a strain energy ratio of at least about 2%.

Vibration damping layer

34

may be a continuous layer, a discontinuous layer, a layer of uniformed or non-uniformed thickness, a lattice network layer, a wound layer, a woven or braided layer, or a laminar layer. The viscoelastic material of vibration damping layer

34

may optionally have adhesive properties, be crosslinked, and further comprise additives such as fibrous and/or particulate materials, curing agents, crosslinking agents, fillers, colorants, processing aids, antioxidants, foaming agents, and mixtures thereof. Specific viscoelastic materials for the present invention include, but are not limited to, vinyl copolymers; polyvinyl acetate and copolymers thereof; acrylics; polyesters; polyurethanes; polyethers; polyamides; polybutadienes; polystyrenes; polyisoprenes; polyethylenes; polyolefins; polyvinyl butyral; styrene/isoprene block copolymers; metallized polyesters; metallized acrylics; epoxies; epoxy and graphite composites; epoxy-acrylate interpenetrating networks; natural and synthetic rubbers; silicon rubbers; nitrile rubbers; butyl rubbers; styrene-butadiene copolymers; piezoelectric ceramics; thermosetting and thermoplastic rubbers; foamed polymers; ionomers; low-density fiber glass; bitumen; air bladders; liquid bladders; and mixtures thereof. The metallized polyesters and acrylics preferably comprise aluminum as the metal. Piezoelectric ceramics particularly allow for specific vibration frequencies to be targeted and selectively damped electronically. Examples of additives and alternative configurations of vibration damping layer

34

are described in U.S. Pat. No. 5,902,656, the disclosure of which is incorporated herein by reference in its entirety. Commercially available viscoelastic materials applicable in the present invention include resilient polymeric materials such as Scotchdamp™ from 3M, Sorbothane® D from Sorbothane, Inc., DYAD® and GP® from Soundcoat Company Inc., Dynamat® from Dynamat Control of North America, Inc., NoViFlex™ Sylomer® (from Pole Star Maritime Group, LLC, and Legetolex™ from Piqua Technologies, Inc.

Another group of suitable viscoelastic materials is low-density granular materials that when coupled to structures for the purpose of reducing structural vibrations, provide a concomitant attenuation in airborne acoustic noises radiated from the structure. Such low-density granular materials include without limitation perlite; vermiculite; polyethylene beads; glass microspheres; expanded polystyrene; nylon flock; ceramics; polymeric elastomers; rubbers; dendritic particles; and mixtures thereof. Preferably, low-density granular materials with dendritic structures and low bulk sound speeds are used for vibration damping layer

34

to maximize damping of low-frequency vibrations and attenuating acoustic noises in golf shafts. Technology associated with the use of these low-density granular materials for damping structural vibrations is described by the trademark name Lodengraf™.

Other choices of materials for vibration damping layer

34

are within the knowledge of one skilled in the art of vibration damping. Vibration damping layer

34

preferably has a thickness of less than about 0.1 inches, more preferably from about 0.0005 inches to about 0.05 inches, and is typically no thicker than cover layer

30

or core layer

32

. The thickness of vibration damping layer

34

may be constant or it may vary along the shaft

12

. For example, vibration damping layer

34

may be thicker in the butt portion

14

and thinner in the tip portion

16

. Vibration damping layer

34

may be placed only in specific regions along the shaft

12

, preferably only in the butt portion

14

, or cover the entire length of the shaft

12

to prevent propagation of vibrations and shocks. In a preferred embodiment, vibration damping layer

34

comprises a thermosetting or thermoplastic resin identical to the resin in core layer

32

. Vibration damping layer

34

preferably covers at least about 5% of the entire length of the shaft, more preferably from about 25% to about 100%, and most preferably from about 50% to about 100%.

In an alternative embodiment of the present invention, as illustrated in

FIG. 7

, an intermediate member

36

and an outer layer

38

in combination may replace cover layer

30

of FIG.

5

. Intermediate member

36

juxtaposes both core layer

32

and outer layer

38

, and preferably is a porous grid, web, mesh, cloth, woven member, braided member, wound member, coil member, continuous member, discontinuous member, or lattice network member formed of an isotropic material, preferably metallic fibers, filaments, wires, strips, or ribbons. Intermediate member

36

may further comprise any of the reinforcement material described above. Any of these filaments and/or fibers may be arranged at different angles with respect to the longitudinal axis of shaft

12

. Preferably, isotropic (metallic) fibers and non-isotropic reinforcement fibers are meshed or inter-woven together. To provide shaft

12

with sufficient stiffness, intermediate layer

36

comprises at least about 50 weight percent of an isotropic or non-isotropic material having a Yong's modulus of greater than about 10 Mpsi. Intermediate layer

36

is preferably embedded within core layer

32

, so that the outer surfaces of the two are flush with each other. In one embodiment, intermediate member

36

has a thickness of preferably less than about 0.2 inches, more preferably between about 0.001 inches and about 0.15 inches. Thickness of intermediate member

36

is also preferred to be less than that of core layer

32

, so that it is partially or fully embedded in the outer surface of core layer

32

. Alternatively, thickness of intermediate member

36

may be greater than or equal to that of core layer

32

, and no less than about 0.2 inches. By integrating, or “fusing,” intermediate member

36

with core layer

32

, torsional rigidity of the shaft

12

is significantly enhanced, yet bending stiffness of shaft

12

is only marginally affected. Bending stiffness, as mentioned before, can be modified by incorporating appropriate amounts of 0° reinforcement fibers into core layer

32

.

Suitable isotropic materials for intermediate member

36

include metals such as titanium, steel, stainless steel, aluminum, tungsten, nickel, copper, zinc, chromium, brass, bronze, magnesium, tin, gold, silver, and the like or alloys thereof. Other useful materials for intermediate member

36

include quasi-isotropic metallic matrix composites. Intermediate member

36

may be applied in any portions of the shaft as a continuous or discontinuous layer having uniformed or non-uniformed thickness. Preferably, intermediate member

36

covers at least the tip portion

16

of the shaft

12

where torsional rigidity is most demanded and desired. The tip portion

16

typically is about 2 inches to about 10 inches in length, measured from the lower tip end upward along the shaft

12

. Overall, intermediate member

36

covers at least about 5% of the length of the shaft

12

, more preferably at least about 75%, and most preferably about 100%. In one embodiment, intermediate member

36

and vibration damping layer

34

may be used together in a multi-layer hybrid shaft, as shown in FIG.

8

. Vibration damping layer

34

may juxtapose both core layer

32

and outer layer

38

. Intermediate member

36

is preferably integrated with, or embedded within, vibration damping layer

34

, having a thickness of no greater than vibration damping layer

34

. Intermediate member

36

and vibration damping layer

34

may be substantially coextensive and have substantially the same thickness, in which case they are combined to form a single hybrid layer that provide both structural strength and vibration damping to the shaft

12

.

In the presence of intermediate member

36

, as in

FIGS. 7 and 8

, it is preferred to cover the entire shaft

12

with an outer layer

38

of an isotropic material for added durability and aesthetic appeal. Suitable isotropic materials for outer layer

38

are metals, preferably the same metal used to form intermediate member

36

, and comprises titanium, steel, stainless steel, aluminum, tungsten, nickel, copper, zinc, chromium, brass, bronze, magnesium, tin, gold, silver, and the like or alloys thereof. Preferably, outer layer

38

has a thickness of less than about 0.05 inches, more preferably between about 0.0004 inches and about 0.03 inches, and most preferably between about 0.001 inches and about 0.02 inches. Conventional methods for metal polishing may be used in fabricating outer layer

38

, as detailed below.

Furthermore, a reinforcing layer

40

formed from an isotropic or quasi-isotropic material may be disposed on the inner surface of core layer

32

, as illustrated in

FIGS. 9 and 10

. Such configurations sandwich core layer

32

between reinforcing layer

40

on the inside and cover layer

30

(

FIG. 9

) or the combination of intermediate member

36

and outer layer

38

(FIG.

10

), forming a classic strained layer vibration damping system that effectively dissipate mechanical energy in the shaft

12

resulted from striking. Reinforcing layer

40

may be continuous or discontinuous, porous or nonporous, similar in construction and/or material composition to cover layer

30

or intermediate member

36

, with a thickness of preferably less than about 0.1 inches, more preferably from about 0.001 inches to about 0.05 inches. Alternatively, reinforcing layer

40

may be one or more discrete elements placed at predetermined locations on the shaft

12

to achieve certain objectives, such as weight adjustment, structural reinforcement, stiffness modification, or kick point adjustment, among others. Reinforcing layer

40

preferably covers a length of at least about 5% of shaft

12

, more preferably it is coextensive to core layer

32

and/or cover layer

30

. Materials suitable for reinforcing layer

40

include those described above for cover layer

30

and intermediate member

36

.

Shaft

12

of the present invention is typically produced in a two-stage process. First, cover layer

30

is pre-formed using conventional methods known to one of ordinary skill in the art, including sheet welding, cold drawing and extrusion. Preferably, cover layer

30

is produced and then air hardened for extra strength using methods described in U.S. Pat. No. 6,293,313. Cover layer

30

may further be coated with one or more metallic elements using any of the metal polishing and deposition methods disclosed below, or coated with one or more non-metallic materials as finishing layers. Certain dimensions of the shaft

12

, including overall length and outer diameters of the butt portion

14

and the tip portion

16

, as well as its general shape (tapered or stepped) are determined by cover layer

30

.

In the second stage, core layer

32

is typically bladder-molded directly onto the inner surface of cover layer

30

. Specifically, as depicted in

FIG. 11

, a metal mandrel

50

is provided, which has a length slightly greater than that of the shaft

12

, and a profile substantially tapered uniformly. A channel network

52

is fabricated within the mandrel

50

to connect multiple openings on the surface of mandrel

50

to an external fluid or gas source (not shown). The mandrel

50

is covered with a bladder

54

made out of a stretchable and impervious material, such as rubber or latex. The thin bladder

54

in the shape of the mandrel

50

may be formed by dipping a counter-form of the mandrel

50

in a liquid bath of latex or similar material. This produces a bladder

54

which fits the mandrel

50

perfectly, and avoids folds and other surface defects. Alternatively, as described in U.S. Pat. No. 6,361,840, the bladder

54

may be formed by injection molding, which allows the bladder wall to have variable thickness, thereby enabling core layer

32

to have variable wall thickness and complex interior profile, or allowing core layer

32

to conform to inner contours of cover layer

30

. Plus, the injection-molded bladder

54

has added advantages of withstanding high compaction pressures, being durable and reusable and therefore cost-effective, and being easy to remove.

Bladder

54

is preferably comprised of an elastomeric, heat-resistant material. Bladder

54

is required to expand but very little when the bladder is pressurized to compress core layer

32

against cover layer

30

, and it must also be stretched and removed from the interior of the finished cured part. Resilient and flexible materials that are suitable to form bladder

54

include, without limitation, silicon rubber, neoprene, polyvinyl chloride, polyurethane esters, polyurethane ethers, olefins, polyesters, polyethylterephthalate, elastomers, polyethylene, polypropylene, latex, thermoplastics, and mixtures thereof. Bladder

54

may be provided using conventional molding techniques such as blow molding, injection molding, rotational molding, thermoforming, vacuum-forming, thermal shrink-wrapping, or the like. It is understood by the skilled artisan that other materials and techniques known or yet unknown may be employed to produce desirable bladder

54

. Bladder

54

may have a single cell or compartment, or a plurality of segregated cells or compartments that can be independently inflated or pressurized, or the multiple cells or compartments are interconnected with each other. Bladder

54

may further have surface features and/or contours such as bumps, ribs, grooves, protrusions, recesses, dimples, and the like that are in linear, helical, interleaving, spiral, scattered, lattice, wavy, or any other patterns. Varying angles and orientation of the features may result in different stiffness and stress resistance for the shaft. During the bladder molding process, these features and/or contours on bladder

54

can create complementary features and/or contours on the inner surface of core layer

32

. In one embodiment, the grooves, recesses and/or dimples are filled with one or more reinforcing materials or reinforcing layer

40

disclosed herein, so that the reinforcing materials or reinforcing layer

40

can be co-molded onto or into core layer

32

in an integrated fashion. Examples of bladder

54

having groove patterns capable of molding integrated ribs on the inner surface of a tubular structure are described in International Publication No. WO 01/97990, the disclosure of which is incorporated herein by reference in its entirety.

The bladder-covered mandrel

50

is then wrapped with resin-impregnated reinforcement fibers to form core layer

32

. Typically, the pre-impregnated fiber sheets (“prepregs”) are draped or “laid up” over the bladder-covered mandrel

50

, so that the uni-directional fibers are aligned at 0° to the longitudinal axis of the shaft

12

. Plies of prepregs having fiber alignment angles of from about 30° to about 150° relative to the shaft axis are preferably used to provide additional torsional stiffness, particularly to critical areas such as the tip portion

16

. Core layer

32

preferably adopts a laminar structure, having 0° prepreg plies interleaving 45° (i.e. +45°) plies and 135° (i.e. −45°) plies, as described in U.S. Pat. No. 5,569,099. Methods for forming core layer

32

in alternative to the sheet-rolling process described above include filament-winding process and braiding process. A filament-rolled shaft

12

is formed by winding fiber bundles of reinforcing fibers (yarns) over the mandrel

50

while reciprocating them along the longitudinal axis of the mandrel

50

. A braided shaft

12

is formed by braiding a plurality of fiber bundles of reinforcing fibers (yarns) or tow prepregs (or yarn prepregs) over the mandrel

50

to cover substantially the entire length of the shaft

12

. In manufacturing any of the shafts, the reinforcing fibers may be impregnated with thermosetting or thermoplastic resins before or after wrapping the fibers around mandrel

50

. The resin of core layer

32

and/or vibration damping layer

34

may be spin-sprayed onto the inner surface of cover layer

30

, or coated onto the outer surface of bladder

54

by dipping. In the case of thermosetting resins, it is critical that the resins remain uncured until the start of the bladder-molding process described below. Otherwise the cured thermosetting resin will be un-moldable. As for thermoplastic resins, they can be uncured, partially cured or fully cured prior to bladder-molding. Partially or fully cure thermoplastic resins may be softened by heat, therefore enabling the molding process.

The pre-formed cover layer

30

is placed securely in a pre-determined position in a mold

56

. Cover layer

30

is secured in its position by the entire interior wall mold

56

of portion of it snuggly pressing around it, or by various clamps, holders, and the like. A pre-assembled core insert is prepared by covering mandrel

50

sequentially with bladder

54

and core layer

32

, the later of which may be constructed from any combinations of prepreg plies known to one of ordinary skill in the art. The pre-assembled core insert is placed into cover layer

30

. Mold

56

is then closed to hold the mandrel

50

firmly in place at one end or both ends, so that the pre-assembled core insert is substantially concentric to cover layer

30

, leaving a space

58

between cover layer

30

and core layer

32

. Typically the space

58

is limited to a minimum in order to lower the expansion of core layer

32

during bladder inflation and resin curing. To produce a shaft of

FIG. 6

,

8

or

10

, a vibration damping layer

34

is further wrapped around core layer

32

on mandrel

50

as part of the pre-assembled core insert prior to placing into cover layer

30

. Deposition methods for vibration damping layer

34

include sheet-rolling, filament-winding, braiding, dip coating, spin spraying, or any others known to the skilled artisan.

Referring to

FIG. 12

, core layer

32

may be molded onto the inner surface of cover layer

30

through, among other methods, bladder-molding. Specifically, heated and pressurized fluid or gas, or heat-expandable foam, bead or paste is forced into bladder

54

via channel network

52

to inflate bladder

54

. Mold

56

, cover layer

30

and optionally mandrel

50

are pre-heated just prior to expansion of bladder

54

and then maintained at a regulated constant temperature during the molding cycle. Bladder

54

expands progressively, pushing core layer

32

outward toward the inner surface of cover layer

30

. Air in space

58

prior to molding is displaced by the outwardly moving core layer

32

and vented out through small openings on mold

56

. The pressurized fluid or gas fills gap

60

left by the expanding bladder

54

. When the outer surface of core layer

32

is in firm contact with the inner surface of cover layer

30

, expansion of bladder

54

ceases, and the internal pressure of bladder

54

reaches a certain stable level, preferably between about 50 psi and about 300 psi. Bladder

54

is maintained at this pressure for a few minutes, allowing the heated thermosetting or thermoplastic resins in core layer

32

to cure, and then depressurized and deflated, while core layer

32

continues to be exposed to heat until at least about 90% cure is achieved. In this embodiment, cover layer

30

is preferably a solid tubular piece with or without any gaps or spaces on its inner surface. The outward movement of core layer

32

, together with optional chemical treatment and/or physical roughening described below, ensures the formation of a tight bond between core layer

32

and cover layer

30

. When core layer

32

is sufficiently cured, the heat is removed and hybrid shaft

12

can then be extracted out of mold

56

. Variables such as duration, temperature, and pressure in each steps above depend upon, among other factors, the nature and reactivity of the resins in core layer

32

, as well as the nature of the material used to form bladder

54

.

The conjoining between the inner surface of cover layer

30

and the outer surface of core layer

32

during the bladder molding process above may involve structural adhesives, contact adhesion, physical bonding, chemical bonding, and the like or a combination thereof. In order to facilitate the bonding between the two layers, it may be desirable to physically and/or chemically roughen the inner surface of cover layer

30

to increase area of contact, or chemically functionalize the inner surface, through processes such as chromate treatment, phosphonation, or silanation, among others. Suitable structural adhesives for bonding between isotropic materials and non-isotropic materials of the present invention include epoxies, acrylics, acrylic/epoxy hybrids, and the like or mixtures thereof. Examples of these structural adhesives are commercially available from 3M of St. Paul, Minn. Two-part reaction-cured epoxies, one-part heat-cured epoxies, and two-part urethane adhesives are sold under the trademark of ScotchWeld™. Moisture-curing polyurethane adhesives are sold under the trademark of Jet-Weld™, double-coated pressure-sensitive all-acrylic foam tapes are sold under the trademark of VHB™, and heat-cured acrylic/epoxy hybrid structural bonding tapes are sold under the trademark of SBT™. Both VHB™ and SBT™ tapes are preferred adhesives, because their materials provide added seals against moisture and corrosion, and they can serve as a replacement for vibration damping layer

34

to diminish vibration generation and propagation in the shaft

12

. Other suitable structural adhesives for the present invention are known to one of ordinary skill in the art, and include hot melts and polyvinyl acetate.

Depending on the nature of the adhesives, they can be coated or wrapped around core layer

32

during the assembly process and then co-molded onto the inner surface of cover layer

30

, or they can be spin-sprayed onto the inner surface of the cover layer

30

. In another embodiment, prepreg plies forming core layer

32

are directly assembled onto mandrel

50

without bladder

54

, seal-wrapped with a scrim-type material, and heat-cured to form core layer

32

. Then a layer of structural adhesives such as the VHB™ or SBT™ tapes is applied over core layer

32

through dip coating, spray coating, tape winding, or sheet wrapping. A volatile material such as mineral spirit can be used to coat the adhesive-covered core layer

32

for lubrication, so that core layer

32

can be easily slid into cover layer

30

. Finally, the jointed cover layer

30

and core layer

32

are co-heated to evaporate off the volatile lubricant, allowing the adhesive to firmly bond cover layer

30

and core layer

32

together to form hybrid shaft

12

of the present invention.

Fabrication of shafts of the present invention using a combination of intermediate member

36

and outer layer

38

as the cover layer are shown in

FIGS. 13 and 14

. Porous intermediate member

36

is first placed with its outer surface firmly pressed against the inner surface of mold

56

in a pre-determined position. Pre-assembled mandrel

50

covered around with bladder

54

, core layer

32

, optional vibration damping layer

34

, and optional adhesive layer is inserted into intermediate member

36

. Mold

56

closes to secure and center the mandrel pre-assembly within intermediate member

36

. Bladder molding ensue, the detail of which is described above. Under the pressure of the expanding bladder

54

, the material of the outer surface of the pre-assembly, may it be core layer

32

, vibration damping layer

34

, or optional adhesive layer, completely fills the gaps and spaces within the porous intermediate member

36

. When the outer surface of the pre-assembly reaches the outer surface of intermediate member

36

, it is stopped by the inner surface of mold

56

. Internal pressure of bladder

54

build up to a steady level in a range of from about 100 psi to about 500 psi. As a result, intermediate member

36

is effectively embedded tightly into the resin matrix of core layer

32

, with its outer surface substantially flush with that of core layer

32

to jointly form a continuous outer surface.

After core layer

32

is allowed to cure, the resulting pre-finished shaft

12

of intermediate member

36

and core layer

32

is removed from mold

56

, and outer layer

38

is applied thereon. Metal coating methods for this step include, but are not limited to, thermal spraying, hot-dip galvanizing, painting, flow coating, electroless deposition, electroplating, chemical vapor deposition, physical vapor deposition, kinetic energy metallization, sputtering, ion implantation, or the like. Thickness of outer layer

38

preferably ranges from about a few layers of molecules to about 0.05 inches, more preferably from about 0.0004 inches to about 0.05 inches, and most preferably from about 0.001 inches to about 0.02 inches. Optionally, selective regions of the shaft

12

, such as the tip portion

16

, may be coated with a thicker outer layer

38

than other regions, thereby imparting desired properties such as extra torsional stiffness and resistance to breakage to the selected regions.

Reinforcing layer

40

may be incorporated into hybrid shaft

12

by embedding it in or depositing it on an inner surface of core layer

32

either during the construction of the pre-assembled core insert, or after core layer

32

is fully cured. In one embodiment, reinforcing layer

40

is a pre-formed, porous and expandable grid, cloth, filament wound layer, or coil layer, in which case it may be wrapped immediately around bladder

54

before lay-up of core layer

32

, and co-molded into shaft

12

with core layer

32

. This way reinforcing layer

40

is partially or fully embedded into the inner surface of core layer

40

. In another embodiment, core layer

32

is first bladder-molded onto cover layer

30

or intermediate member

36

. Reinforcing layer

40

is then formed by depositing one or more metal element on the inner surface of core layer

32

using any of the methods mentioned above for fabrication outer layer

38

. In an alternative embodiment, reinforcing layer

40

is a solid sheath, a discontinuous layer, or a lattice network layer wrapped directly on mandrel

50

. Core layer

32

and optional vibration damping layer

34

are laid up on reinforcing layer

40

to form a pre-assembled core insert. The core insert is wrapped with a scrim-type layer and fully cured in an oven as a typical composite shaft. Then the cured core insert is coated with a layer of structural adhesive, lubricated with mineral spirit, and placed snuggly into cover layer

30

. Heat is applied to evaporate off the mineral spirit so that the adhesive bonds the cured insert to cover layer

30

to yield hybrid shaft

12

.

After shaft

12

is molded and optionally coated with outer layer

38

, certain cosmetic steps such as finishing, painting and varnishing are performed. Desirably, any burrs of resin located along the mold joint are removed by grinding or other methods. Painting can be followed by a post-curing operation, which entails heating shaft

12

at a temperature of between about 80° C. and about 180° C. for approximately 25 minutes to 2 hours. This step completes the curing of shaft

12

and releases the volatile organic compounds and hazardous air pollutants from within core layer

32

.

Any of the layers disclosed herein for hybrid shaft

12

may further include one or more layers to achieve certain functions or properties. For example, cover layer

30

may be coated with one or more metallic or non-metallic layers for enhanced appearance or weather-proofing. Core layer

32

may include multiple plies of prepreg having reinforcement fibers aligned at different angles to the shaft axis for added strength and/or stiffness. Shaft

12

may further incorporate one or more decorative layers to enhance aesthetics, such as those disclosed in U.S. Pat. No. 5,773,154.

All patents and patent applications cited in the foregoing text are expressly incorporated herein by reference in their entirety.

The invention described and claimed herein is not to be limited in scope by the specific embodiments herein disclosed, since these embodiments are intended as illustrations of several aspects of the invention. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.

Number	Name	Date	Kind
4084819	Van Auken	Apr 1978	A
4097626	Tennent	Jun 1978	A
4188032	Yanagioka	Feb 1980	A
4539253	Hirschbuehler et al.	Sep 1985	A
4961576	Meredith	Oct 1990	A
5028464	Shigetoh	Jul 1991	A
5083780	Walton et al.	Jan 1992	A
5259614	Greer	Nov 1993	A
5324032	Minami	Jun 1994	A
5427373	Kusumoto	Jun 1995	A
5437450	Akatsuka et al.	Aug 1995	A
5599242	Solviche et al.	Feb 1997	A
5607364	Hedrick et al.	Mar 1997	A
5755826	Beach et al.	May 1998	A
5773154	Takada	Jun 1998	A
5904628	MacKay, Jr. et al.	May 1999	A
5924936	Penley	Jul 1999	A
6139444	Renard et al.	Oct 2000	A
6287696	Noda et al.	Sep 2001	B1
6302806	Hsu	Oct 2001	B1
20020119829	Cheng	Aug 2002	A1

Number	Date	Country
2227418	Jan 1990	GB
2001-246029	Sep 2001	JP
2002-126142	May 2002	JP
2002126142	Aug 2002	JP
2002-253714	Sep 2002	JP
WO 0197990	Dec 2001	WO

Hybrid golf club shaft

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

US Referenced Citations (21)

Foreign Referenced Citations (6)