Patent Publication Number: US-2011065526-A1

Title: Golf club shaft and golf club

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority on Japanese Patent Application No. 2009-210469 filed Sep. 11, 2009, which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a golf club shaft that is formed using fiber-reinforced resins, and to a golf club including the same, and more particularly, relates to a golf club shaft and a golf club using the same that has improved vibration characteristics at the time of impact and stability of a ball that is struck. 
     Among conventional shafts made from a hollow tubular body as a shaft for a golf club with improved vibration characteristics at the time of impact, one has been proposed in which the hollow tubular body of the shaft is filled with a foam (Japanese Patent Application Publication No. 6-182007). 
     Although when a player makes a shot that is off-center on the club head, the shaft vibrates irregularly and an unpleasant numbing sensation occurs, because the hollow tubular body of the golf club shaft in the Japanese Patent is filled with a foam, the vibration characteristics of the foam cause a reduction in the irregular vibration of the shaft in the case of an off-center impact, and thereby causes a reduction in the unpleasant numbing sensation. 
     However, although the golf club shaft of the Japanese Patent can reduce the irregular vibration of the shaft at the time of an off-center impact by the vibration-absorbing characteristics of the foam, it did not have a function that stabilizes the struck ball. 
     SUMMARY OF THE INVENTION 
     The present invention was made in view of the above circumstances, and the present invention has as an object to provide a shaft for a golf club and a golf club that have a shaft vibration-attenuating function at the time of impact and a function of stabilizing a struck ball. 
     In order to achieve the above object, the present invention provides, as described below, a first aspect of the invention of a shaft for a golf club, and a second aspect and a third aspect of the invention of a golf club. 
     The first aspect of the invention is a golf club shaft including a plurality of resin layers as the plurality of resin layers including an inner bias fiber-reinforced resin layer with reinforcing fibers aligned along a first direction that is inclined with respect to the shaft axial direction; an outer bias fiber-reinforced resin layer along a second direction is inclined with respect to the shaft axial direction opposite to the first direction; and a vibration-damping material sheet layer having a vertical-direction length of about 110 mm to about 150 mm, or more preferably from about 120 mm to about 140 mm, being interposed between the inner bias layer and the outer bias layer and being positioned at a range from about 55% to about 80% of the shaft length, or more preferably from about 56% to about 76%, from a shaft tip. 
     The second aspect of the invention is a golf club using a golf club shaft including a plurality of resin layers as the plurality of resin layers including an inner bias fiber-reinforced resin layer with reinforcing fibers aligned along a first direction that is inclined with respect to the shaft axial direction; an outer bias fiber-reinforced resin layer along a second direction is inclined with respect to the shaft axial direction opposite to the first direction; and a vibration-damping material sheet layer having a vertical length of about 110 mm to about 150 mm, or more preferably from about 120 mm to about 130 mm, being interposed between the inner bias layer and the outer bias layer, and being positioned from about 235 mm to about 270 mm, or more preferably from about 245 mm to about 260 mm, from a butt end of the shaft taken as the rear end in the vertical direction. 
     The third aspect of the invention is a golf club using a golf club shaft including a plurality of layers as the plurality of resin layers including an inner bias fiber-reinforced resin layer with reinforcing fibers aligned along a first direction that is inclined with respect to the shaft axial direction; an outer bias fiber-reinforced resin layer with reinforcing fibers aligned along a second direction is inclined with respect to the shaft axial direction opposite to the first direction; and a vibration-damping material sheet layer having a vertical length of about 110 mm to about 150 mm, or more preferably from about 120 mm to about 140 mm, being interposed between the inner bias layer and the outer bias layer, and being positioned at a region of a position of the end of the grip attachment location is taken as the rear end in the vertical direction. 
     Because the golf club shaft of the present invention basically has the region of the position of the end of the grip attachment location as the rear end in the vertical direction and a vibration-damping material sheet with a vertical-direction length of about 110 mm to about 150 mm, the vibration-attenuating action of the vibration-damping material sheet reduces the vibration of the shaft at the time of impact and attenuates the vibration quickly, thereby improving the impact feel. The golf club shaft of the present invention also has a low rigidity in the part in which the vibration-damping material sheet is disposed, and as a result of the ease of flexure in the location in which the vibration-damping material sheet is disposed, the overall shaft flexes, making the shaft easy to swing and stabilizing the ball that is struck. 
     The present invention will now be described in further detail. The golf club shaft according to the present invention has a plurality of fiber-reinforced resin layers in which the reinforcing fibers are aligned in one direction. It is possible to use, for example, carbon fibers, glass fibers, metal fibers, aramid fibers, silicon carbide fibers, alumina fibers, and boron fibers as the above-noted reinforcing fibers. As a thermally cured resin of the reinforced fiber resin layer, it is possible to use an epoxy resin, a phenol resin, an unsaturated polyester resin or the like, or a combination of a plurality thereof. Additionally, it is possible to use a curing agent, a curing accelerator, a filler, a parting agent, or a pigment, or the like as a supplemental substance. 
     The fiber-reinforced resin layer of the shaft according to the present invention can be formed, for example, by a sheet winding method of winding a prepreg sheet around a metal core (mandril) and subjecting this to thermal curing. As the prepreg sheet, it is possible to use a roving, cloth, or mat that has been aligned in parallel and impregnated in a thermally cured resin. The above-noted inner bias layer and outer bias layer are essential as fiber-reinforced resin layers in the present invention. The appropriate angle between the fiber direction of the inner bias layer and outer bias layer and the shaft axial direction is from about 35° to about 55°. 
     In the second and third inventions, a vibration-damping material is disposed in the range noted above with regard to the first invention, and with regard to the second and third invention a vibration-damping material sheet having a vertical-direction length of about 110 mm to about 150 mm is disposed between the inner bias layer and the outer bias layer, with the above-noted position as the vertical-direction rear end regard. In this case, it is preferable to use a polyester-based resin composition made of a polyester-based resin into which an at least one of an electrically conductive material and a filler has been dispersed are prepared as the vibration-damping material sheet. The above-noted polyester-based resin composition efficiently absorbs vibration energy and has a superior vibration-damping effect. As the above-noted polyester-based resin, it is possible to use a polyester-based resin having a dicarboxylic acid component and diol component as unit components. As the above-noted electrically conductive material, it is possible to use as inorganic materials, for example, silver, iron, lead, copper, a copper alloy, nickel, a low melting point metal powder or metal fiber; copper or silver microparticles covered with a precious metal; microparticles or whiskers of a metal oxide such as tin oxide, zinc oxide, or indium oxide; electrically conductive carbon powders, such as various types of carbon black or carbon nanotubes; and carbon fibers such as PAN carbon fibers, pitch-based carbon fibers, and vapor-phase grown graphite and the like. Organic materials that can be used are anti-static agents of the low polymer surfactant type; high polymer anti-static agents; electrically conductive polymers such as polypyrrole and polyanyline; and polymer microparticles that have been covered by a metal. As the filler mentioned above, it is possible to use, for example, mica flakes, glass pieces, sericite, graphite, talc, aluminum flakes, boron nitride, molybdenum sulfide, and flake-type fillers such as scalelike filler. 
     As the vibration-damping material forming the vibration-damping material sheet, it is possible to preferably use materials disclosed in the Japanese Patent Application Publication No. 2006-52377 and Japanese Patent Application Publication No. 2008-189854, which are incorporated by reference, and more specifically, it is preferable to use Neofade (product name) made by Mitsubishi Gas Chemical Company, Inc. 
     The layer made of the inner bias layer, the outer bias layer, and the vibration-damping material layer may be formed by laminating the inner bias layer prepreg sheet and the outer bias layer prepreg sheet with the vibration-damping material layer sheet interposed therebetween, and winding the laminate of the inner bias layer prepreg sheet and the outer bias layer prepreg sheet around a metal core. That is, whereas it is usual to use as the vibration-damping material sheet a sheet made of a polyester resin composition that does not have pressure-sensitive adhesion, even in the case as noted above, in which the inner bias layer prepreg sheet and the outer bias layer prepreg sheet, in between which is sandwiched the vibration-damping material sheet, are wound around the metal core, by sandwiching the vibration-damping material sheet between the inner bias layer and the outer bias layer, even if a sheet without pressure-sensitive adhesion is used as the vibration-damping sheet, it is possible to prevent peeling away of the vibration-damping material sheet. 
     It is preferable that the vibration-damping material sheet be disposed as the position of the beginning part of the winding of the inner bias layer prepreg sheet and the outer bias layer prepreg sheet around the metal core. By doing this, because the vibration-damping material sheet is sandwiched between the inner bias layer and the outer bias layer, it is possible to minimize the reduction in the performance of the shaft even if there is insufficient holding between the fiber-reinforced resin layers and the vibration-damping material sheet. 
     Additionally, in the case of winding a laminate of the inner bias layer prepreg sheet and the outer bias layer prepreg sheet with the vibration-damping material sheet sandwiched therebetween around a metal core as noted above, it is appropriate to wind the vibration-damping material sheet one turn around the metal core and wind the laminate of the inner bias layer prepreg sheet and the outer bias layer prepreg sheet around the metal core four to six turns. By doing this, the vibration-damping material sheet is wound close to the metal core, surface unevenness of the shaft surface is reduced and, because the vibration-damping material sheet is surrounded by and sandwiched between the inner bias layer prepreg sheet and the outer bias layer prepreg sheet, it is difficult for the position of the vibration-damping material sheet to shift at the time of molding, and it is possible to achieve the effect of it being difficult for the vibration-damping material sheet to peel away during use. 
     In the present invention, in the case of using a layer made by the inner bias layer, the outer bias layer, and the vibration-damping material layer as the inner layer of the shaft, if necessary a straight layer having a fiber direction that coincides with the shaft axial direction or a hoop layer having a fiber direction that is perpendicular to the shaft axial direction or the like may be formed on the outside of the outer bias layer. Additionally, painting may be done to the outermost layer of the shaft. 
     The shaft for a golf club and golf club using same according to the present invention achieves the following effects. Firstly, by virtue of the vibration-attenuating action of the vibration-damping material sheet, the vibration of the shaft at the time of impact is reduced and the vibration attenuates quickly, so that the feel of impact is improved. Secondly, because of the low rigidity in the part in which the vibration-damping material sheet is disposed, flexure occurs easily in the location in which the vibration-damping material sheet is disposed, and the overall shaft flexes, making the shaft easy to swing and stabilizing the ball that is struck. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic front elevation view showing one embodiment of a shaft for a golf club according to the present invention. 
         FIG. 2  is a schematic enlarged cross-sectional view along the line A-A of  FIG. 1 . 
         FIG. 3  is a view showing the size of an example of a vibration-damping shaft. 
         FIGS. 4  ( a ) and  4  ( b ) are views showing an example of a process for manufacturing the shaft for a golf club of  FIG. 1 . 
         FIGS. 5  ( a ) and  5  ( b ) are graphs showing the vibration-attenuating effect of the shaft for a golf club of  FIG. 1 . 
         FIG. 6  is a graph showing the rigidity distribution of the shaft for a golf club of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Although embodiments of the present invention are described below, with reference made to the accompanying drawings, the present invention is not limited to these embodiments.  FIG. 1  is a conceptual front elevation showing an embodiment of a shaft for a golf club according to the present invention, and  FIG. 2  is a conceptual enlarged cross-sectional view along the line A-A of  FIG. 1 , the example shown being a men&#39;s driver. 
     The golf club shaft  10  of this example had, as fiber-reinforced resin layers in sequence from the inside, an inner bias layer  12  having a fiber direction that was inclined with respect to the shaft axial direction, an outer bias layer  14  having a fiber direction that was inclined with respect to the shaft axial direction in a direction opposite from that of the inner bias layer  12 , and a straight layer  16  having a fiber direction that coincides with the shaft axial direction. Each of the fiber-reinforced resin layers  12 ,  14 , and  16  was formed by winding a single prepreg sheet in the form of a sheet made by impregnating a carbon fiber (roving) that had been aligned in parallel with an epoxy resin or an unsaturated polyester resin from four to six times around a metal core. However, the inner bias layer  12  and the outer bias layer  14  were formed by winding after laminating the prepreg sheets that form same beforehand. 
     In the golf club shaft  10  of this example, with the end position region of the attachment location of the grip  18  taken as the vertical-direction rear end  20 , a vibration-damping material sheet layer  22  having a vertical-direction height a of about 130 mm and made of a polyester-based resin composition (Neofade (product name) made by Mitsubishi Gas Chemical Company, Inc.) of a polyester-based resin into which at least one of an electrically conductive material and a filler had been dispersed was interposed between the inner bias layer  12  and the outer bias layer  14 . The location of this vibration-damping material sheet layer  22  was a position range from 64.1% to 75.2% of the shaft length b from the shaft tip end (i.e., shaft end on the head side), and the position of the vertical-direction rear end  20  of the vibration-damping material sheet layer  22  was a position that was about 257 mm (distance d) from the shaft butt end (i.e., shaft end on the grip side). The above-noted 64.1% was the value of the leading end position of the vibration-damping material sheet layer  22  (calculated by the formula (c-a)/b×100), and the 7.52% was the value of the rear end position of the vibration-damping material sheet layer  22  (calculated by the formula c/b×100). The vibration-damping material sheet layer  22  was formed by one winding of a vibration-damping material one time around a metal core. The vibration-damping material sheet was, as shown in  FIG. 3 , an equal-foot trapezoidal shape, the long side of which was about 130 mm, the short side of which was about 30 mm, the width of which was about 40 mm, and the thickness of which was 0.145 mm. 
     The above example was that of a men&#39;s driver, and the locations of disposition of the vibration-damping sheet layer in this shift and other shafts were as shown below in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Overall 
                   
               
               
                   
                 shaft 
               
               
                   
                 length 
                 Vibration-damping sheet 
               
               
                   
                 (mm) 
                 layer disposition location 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Shafts for a men&#39;s club 
                   
                   
               
               
                 For a wood club 
                 1170 
                 Location 750 to 880 mm from the end 
               
               
                 For a utility club 
                 1065 
                 Location 610 to 740 mm from the end 
               
               
                 For an iron club 
                 990 
                 Location 580 to 710 mm from the end 
               
               
                 Shafts for a women&#39;s 
               
               
                 club 
               
               
                 For a driver 
                 1145 
                 Location 720 to 850 mm from the end 
               
               
                 For a fairway wood 
                 1080 
                 Location 660 to 790 mm from the end 
               
               
                 For a utility club 
                 985 
                 Location from 590 to 720 mm from the 
               
               
                   
                   
                 end 
               
               
                 For an iron club 
                 935 
                 Location from 530 to 660 mm from the 
               
               
                   
                   
                 end 
               
               
                   
               
            
           
         
       
     
     The golf club shaft of this example could, for example, be manufactured by the sheet-winding method, using the following prepreg sheets. 
     (1) As shown in  FIG. 4(   a ), a inner bias layer prepreg sheet  34  having a fiber direction  30  that was at an inclination of 45° with respect to the shaft axial direction  32 , an outer bias layer prepreg sheet  36  having a fiber direction  30  that was at an inclination of 45° with respect to the shaft axial direction in the opposite direction from the inner bias layer prepreg sheet  34 , a straight layer prepreg sheet  38  having a fiber direction  30  that coincides with the shaft axial direction  32 , and vibration-damping material sheet  40  made of a polyester-based resin composition made of a polyester-based resin into which at least one of an electrically conductive material and a filler had been dispersed were prepared. 
     (2) As shown in  FIG. 4(   b ), the inner bias layer prepreg sheet  34  and the outer bias layer prepreg sheet  36  were laminated with the vibration-damping material sheet  40  interposed therebetween. In this case, the vibration-damping material sheet  40  was disposed at the beginning part of winding around the metal core  42 . 
     (3) After winding the inner bias layer prepreg sheet  34  and the outer bias layer prepreg sheet  36  around the metal core  42 , the straight layer prepreg sheet  38  was wound around the outside thereof, and tape was further wound around the outside thereof. 
     (4) The prepreg sheets were thermally cured in a high-temperature oven. 
     (5) After forming the shaft, the metal core and tape were removed, and the outer peripheral surface of the straight layer was made smooth by filing, after which the outer peripheral surface of the straight layer was painted. 
       FIG. 5  shows the vibration characteristics of the golf club shaft of  FIG. 1 .  FIG. 5(   a ) shows the vibration of the shaft after it was used to manufacture a golf club, measured by an accelerometer, with the club suspended vertically and a hammer used to strike the head at an off-center location. The off-center location was a location about 20 mm distant in the toe direction from the center of the face surface. From  FIG. 5(   a ), it could be seen that the shaft of this example, provided with a vibration-damping material sheet layer, not only had small vibration of the shaft at the time of impact, but also exhibits fast attenuation of vibration. 
       FIG. 6  shows the rigidity distribution of the golf club shaft of  FIG. 1 . From  FIG. 6 , it could be seen that the shaft of this example, provided with a vibration-damping material sheet layer, had a lower rigidity at the location of the vibration-damping material sheet, about 750 to about 880 mm from the shaft end, than one in which a vibration-damping material sheet layer was not disposed, so that the entire shaft flexes and the struck ball is stabilized.