Abstract:
A golf club shaft made of a composite of a fiber material and a synthetic resin material, wherein the fiber material includes triaxial fabric layers which are located at least on the butt end side and the tip end side of the golf club shaft. Either the fiber density, the kind of the fiber, the physical property of the fiber, or a combination of two or more thereof, of yarn paths of three directions that form the triaxial fabric layers is varied with respect to the longitudinal axis of the shaft in accordance with a required specification of the shaft.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a golf club shaft made of a composite of a fiber material and a synthetic resin material. 
     2. Description of the Related Art 
     Recently, a golf club shaft is made of a combination of a fiber material such as glass fiber or carbon fiber, and a compound synthetic resin. It is known for fiber material to be formed as a diagonal fiber layer, an axial fiber layer, a triaxial fabric layer; or a combination thereof. A diagonal fiber layer refers to a fiber layer in which pairs of yarn paths defined by fiber bundles are inclined in opposite directions with respect to the longitudinal axis of the shaft. An axial fiber layer refers to a fiber layer in which the yarn paths extend in parallel with the longitudinal axis of the shaft. A triaxial fabric layer refers to a fabric layer in which yarns are woven so that three directions of the yarn paths form approximately 60° or 120°. These fiber or fabric materials are provided with thermoplastic resin or thermosetting resin impregnated therein to form a prepreg, which is then wound by several turns, and is hardened to obtain a golf club shaft. 
     The assignee of the present application has proposed a golf club shaft made of a triaxial fabric (layer) in Japanese Utility Model Registration No. 2,553,611 or No. 2,553,612, and has marketed the same. In these utility model applications, it was considered essential or preferable that the triaxial fabric layer be uniformly provided over the entire length of the shaft, and one of the yarn paths to extend in the axial direction of the shaft. 
     However, it has been found by recent studies of triaxial fabrics that it is not necessary for the triaxial fabric layer to be uniformly provided over the entire length of the shaft, nor for one of the yarn paths to extend in the axial direction of the shaft; furthermore, triaxial fabrics having a variety of specifications can be advantageously used to respond to various requirements of a golf club shaft. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a golf club shaft made of a composite of a fiber material and a synthetic resin material, wherein the bending rigidity, the torsional rigidity or the deformation rigidity (rigidity against the partial collapse of the circular shape in section), etc., is achieved so as to be varied in accordance with need in the direction of the longitudinal axis of the shaft. 
     To achieve the object mentioned above, according to an aspect of the present invention, there is provided a golf club shaft made of a composite of a fiber material and a synthetic resin material, wherein the fiber material is composed of triaxial fabric layers having three yarn paths of three directions which are located at least on the butt end side and the tip end side of the golf club shaft; wherein either the fiber density, the kind of fiber, the physical property of the fiber, or a combination of two or more thereof, of the yarn paths of three directions that form the triaxial fabric layers, is varied with respect to the longitudinal axis of the shaft in accordance with a required specification of the shaft. 
     Preferably, the fiber density of the triaxial fabric layers is determined based on either the specification of the triaxial fabric layer, the arrangement of the triaxial fabric layer, or both the specification and arrangement thereof. 
     Preferably, the specification of the triaxial fabric layers is determined based on either the kind, the number, the distance, the thickness, or a combination of one or more thereof, of the fiber of the yarn paths of three directions. 
     Preferably, the yarn paths in three directions have different numbers of fibers. 
     The arrangement of the triaxial fabric layers can be such that a plurality of triaxial fabric layers having different winding radii in the axial direction of the shaft mutually overlap each other in part. 
     Alternatively, the arrangement of the triaxial fabric layers is such that the triaxial fabric layers are spaced from one another in the axial direction of the shaft. 
     Alternatively, a plurality of triaxial fabric layers which are multi-layered are provided so that the direction of the yarn paths of the triaxial fabric layers are different from one another. 
     Preferably, the triaxial fabric layers includes at least one layer which extends along the overall length of said golf club shaft and another triaxial fabric layer which does not extend along the overall length of the golf club shaft. 
     Preferably, the fiber of the triaxial fabric layers is selected from one or more of the following: carbon fiber, alumina fiber, aramid fiber, tyranno fiber, amorphous fiber, or glass fiber. 
     Preferably, the physical property of the triaxial fabric layers includes either a high tensile strength, a high tensile elasticity modulus, or a combination of both. 
     The present disclosure relates to subject matter contained in Japanese Patent Application No.10-117161 (filed on Apr. 27, 1998) and Japanese Patent Application No. 10-155842 (filed on Jun. 4, 1998) which are expressly incorporated herein by reference in their entireties. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be discussed below in detail with reference to the accompanying drawings, in which: 
     FIG. 1 is a sectional view of a skeleton of a golf club shaft made of a triaxial fabric, according to an embodiment of the present invention; 
     FIG. 1A is a fragmentary perspective view of a portion of the golf club shaft of FIG. 1; 
     FIG. 2 is a sectional view of a skeleton of a golf club shaft made of a triaxial fabric, according to another embodiment of the present invention; 
     FIG. 3 is a sectional view of a skeleton of a golf club shaft made of a triaxial fabric, according to another embodiment of the present invention; 
     FIG. 4 is a sectional view of a skeleton of a golf club shaft made of a triaxial fabric, according to another embodiment of the present invention; 
     FIG. 5 is a schematic perspective view of an example of a central prepreg consisting of a diagonal fabric prepreg and a longitudinal fabric prepreg; 
     FIG. 6 is a schematic plan view of yarn paths of a triaxial fabric used in a golf club shaft according to the present invention; and 
     FIGS. 7 through 16 are plan views of different examples of a triaxial fabric usable in the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A triaxial fabric which constitutes a triaxial fabric prepreg  10  is formed by weaving threads of the three-direction yarn paths x, y, and z which form approximately 60° or 120° therebetween, as schematically shown in FIG.  6 . The fabric prepreg is in the form of a sheet of thermoplastic or thermosetting resin with which the fabric is impregnated. Since the directions of the fibers in the prepreg are fixed by the resin, no accidental movement of the direction of the fibers occurs. Epoxy resin, unsaturated polyester resin, phenyl resin, vinyl ester resin, or peek resin (poly ether ether ketone resin), can be used as the resin for the prepreg. 
     Carbon fiber, alumina fiber, aramid fiber, tyrano fiber (trade name; Si—Ti—C—O fiber, fiber with a silicon-titanium-carbon-oxygen base), amorphous fiber, or a glass fiber can be used as the fiber to form the yarn paths x, y and z. The carbon fiber to be used can be either PAN(poly crylonitrile)-based carbon fiber or pitch-based carbon fiber. The above mentioned fibers have different physical properties. For the same fiber, it is possible to provide different tensile strengths or tensile elasticity moduli. 
     The thickness of the fiber (thread) which constitutes the yarn paths x, y and z is in the range of 0.1 to 3 K (1 K=7 μm×1000). The number (pitch) of the implanted fibers for a unit length is in the range of 2 to 20 fibers per centimeter. Several kinds of triaxial fabric prepregs  10  are prepared by appropriately combining the thicknesses of a number of fibers. 
     FIGS. 7 through 16 show examples of the triaxial fabrics. These examples have been proposed in U.S. Pat. No. RE28,155 (U.S. Ser. No. 515,028). In FIG. 7, the yarn paths x, y and z are each defined by a single thread and are spaced from one another to define therebetween spaces s. In FIG. 8, the yarn path x is defined by two threads and the yarn paths y and z are each defined by a single thread; the yarn paths x, y and z are spaced from one another to define therebetween space s. In FIG. 9, the yarn paths x, y and z are each defined by two threads and there is no space s therebetween. In FIG. 10, the number of threads of each yarn path is the same as that in FIG. 9, but the way the threads of the yarn paths are woven (the lay of the threads) is different. In FIG. 11, the yarn path y is defined by two threads and the yarn paths x and z are each defined by a single thread; the way the threads of the yarn paths y 1  and y 2  are woven is different, the yarn paths x, y and z are spaced from one another to define therebetween spaces s. In FIG. 12, the way the threads of the yarn paths x 1 , x 2  and y 1 , y 2  are woven is different again, the yarn paths x, y and z are each defined by two threads and the yarn paths x, y and z are spaced from one another to define therebetween spaces s. In FIG. 13, the yarn paths x, y and z are each defined by a single thread, the threads are tightly woven so that there is no space therebetween. 
     In FIG. 14, the way the threads of the yarn paths x 1  and x 2  are woven is different, the yarn path x is defined by two threads and the yarn paths y and z are each defined by a single thread; there are spaces between the yarn paths. In FIG. 15 which shows an arrangement similar to FIG. 14, there is no space between the yarn paths. In FIG. 16, the adjacent yarn paths x are spaced from one another and there is no space between the yarn paths y or z. The strength in the direction x is less than that in the direction y or z. 
     The examples mentioned above can be applied to the triaxial fabric prepreg. Triaxial fabric prepregs other than those shown in the drawings can be used. The angle defined between the yarn paths x, y and z is not necessarily limited to 60° or 120°. 
     FIG. 1 shows a golf club shaft using triaxial fabric prepregs in the form of discrete units  10 , each of which is wound into a tubular shape, having different diameters, and the same is wound around a core member. A center prepreg  20 A which is made of a diagonal fiber prepreg and/or longitudinal prepreg is wound around a core over the overall length of the shaft. A plurality of a predetermined length of tubular triaxial fabric prepregs  10  having different diameters are step-wise wound around the central prepreg  20 A, so that the adjacent triaxial fabric prepregs  10  partly overlap in the axial direction. It is possible to further provide an isometric tubular triaxial fabric prepreg layer  30  over the overall length of the shaft as indicated by phantom lines. As shown in FIG. 1A, the triaxial fabric of the units  10  may have yarn paths directions different from those of the triaxial fabric of the prepeg layer  30 . 
     FIG. 5 shows an example of the central prepreg  20 A which is made of a tubular diagonal fiber prepreg  21  and a tubular longitudinal fiber prepreg  22 . 
     FIG. 2 shows a golf club shaft comprising a plurality of a predetermined length of tubular triaxial fabric prepregs  10  and an outer prepreg  20 B which is located outside of the tubular triaxial fabrics  10 . The adjacent triaxial fabric prepregs  10  having different diameters are partly overlapped in the axial direction as same as the example shown in FIG.  1 . 
     The prepregs  10 ,  20 A,  20 B and  30  wound around a core member are thereafter hardened to form a golf club shaft. Although the golf club shaft thus obtained is light, the user would feel as if it were a steel shaft. If different specifications or properties of triaxial fabric prepregs  10  are used, a variety of fiber density distributions in the axial direction can be provided. 
     FIG. 3 shows an embodiment in which the triaxial fabric prepregs  10  of a predetermined length are spaced and wound around the central prepreg  20 A. The specification of the triaxial fabric prepregs  10 , the distance therebetween and/or the length thereof can be made different, to vary the fiber density in the axial direction, or the kind or physical property of the fiber can be made so as to be non-uniform in the axial direction to vary the bending rigidity, torsional rigidity or deformation rigidity (rigidity against the partial collapse of the circular shape in section), etc., in the axial direction. 
     FIG. 4 shows an embodiment in which the outer prepreg  20 B is wound onto the tubular triaxial fabric prepregs  10  which are spaced at a predetermined distance from one another in the axial direction, unlike the embodiment shown in FIG. 3 in which the tubular triaxial prepregs  10  are wound onto the tubular central prepreg (diagonal fiber prepreg and/or longitudinal fiber prepreg)  20 A. Alternatively, it is also possible to provide the diagonal fiber prepreg  20 A and/or the longitudinal fiber prepreg  20 B in and around the tubular triaxial prepregs  10 . The embodiments illustrated in FIGS. 2 and 4 can be advantageously applied to an internal pressure molding process, in which the coiled prepregs are disposed within a molding die and the molding is carried out while pressuring the center cavity portion thereof. Consequently, a golf club shaft having a smooth or flat outer surface can be obtained. 
     In the above-mentioned embodiments, as indicated by phantom lines, it is possible to provide an isometric tubular triaxial fabric prepreg  30  over the overall length of the shaft as mentioned above. The isometric tubular triaxial fabric prepreg  30  can be provided in addition to the central prepreg  20 A or the outer prepreg  20 B or it can be provided in place of the central prepreg  20 A or the outer prepreg  20 B. The tubular triaxial fabric prepregs  10  can be made of plural plies of prepregs (multi-layered prepregs). 
     In short, according to the most significant feature of the present invention, either the fiber density, the kind of the fiber, the physical property of the fiber, or a combination of these factors, of the three-directional yarn paths of the tubular triaxial fabric prepreg  10 , is made non-uniform in the axial direction, so that different properties of golf club shafts can be obtained. Presence or absence of other layers of the golf club shaft or the structure thereof is not the subject of the present invention. 
     As can be understood from the above discussion, according to the present invention, the triaxial fabric layers are used, and either the fiber density, the kind of the fiber, the physical property of the fiber of the triaxial fabric layers, or a combination of these factors, is made non-uniform in the axial direction so as to meet required specifications of the shaft.