Abstract:
According to an aspect of this invention, there is provided a golf club shaft including a prepreg containing a carbon fiber, wherein the prepreg is winded and cured, and a winding thickness of the prepreg on a striking face is larger than a winding thickness of the prepreg on any other portion.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a golf club shaft, and more specifically, to a golf club shaft made of fiber-reinforced resin. Further, the present invention relates to a golf club having the golf club shaft. 
         [0003]    2. Description of the Related Art 
         [0004]    Golf club shafts may be classified into what are called a steel shafts and carbon shafts. The carbon shaft is widely used in view of lightness, the high degree of design freedom and the like. 
         [0005]    The carbon shaft is made of fiber-reinforced resin in which a carbon fiber is used as a main fiber. As a method of manufacturing the carbon shaft, a sheet winding method is known (see JP-A-2010-259694). In this manufacturing method, a prepreg sheet is wound on a mandrel (core bar) and a wrapping tape is further wound thereon. Then the prepreg is heated to be cured, thereby making the carbon shaft. 
         [0006]    Since a golf club has large kinetic energy as a head end on which a head is fixed is heavy, it is possible to give a large initial velocity to a ball at the time of swing, thereby making it possible to increase a carry of the ball. However, if only the head end is heavy, the center of gravity of the club is excessively inclined to the head end, and thus, the swing becomes hard. For this reason, when the head end of the shaft is made heavy, a grip end of a base is also made heavy. Further, if the head end and the grip end are heavy in this way and an intermediate portion is light, a follow-through at the time of swing is enhanced. In this way, in the golf club, since the carry of the ball and the swing performance are changed according to the weight distribution on the head end and the grip end, the weight adjustment on both the sides has been performed at the time of golf club design in the related art. 
         [0007]    Since the weight adjustment becomes different according to physical strengths or preferences of players, it is necessary to prepare various heads and shafts. However, to prepare the various heads and shafts having different weights causes an increase in manufacturing cost and storage cost. Thus, the weight adjustment has been performed by a simple method in which a plurality of types of heads and shafts having different weights are made, and then, a lead plate is attached to the head in a case where the head end is heavy and a lead plate is attached to the inside of the grip of the shaft in a case where the grip end is heavy. 
         [0008]    If the weight on the grip end of the carbon shaft is made heavy due to the lead plate attachment, the weight of the shaft is lighter than that of a metal shaft made of a metallic tube in the related art. Further, since the lead plate having a large specific gravity can be only locally attached, it is difficult to increase the weight of the entire grip end, and thus, the rotational moment is changed according to the grip position of a player. 
       SUMMARY 
       [0009]    An object of the invention is to provide a golf club shaft in which the weight on the striking face is increased by distributing, on the striking face, a large amount of prepregs where carbon fibers are distributed, and a golf club that uses the golf club shaft. 
         [0010]    According to an aspect of the invention, there is provided a golf club shaft including a prepreg containing a carbon fiber, wherein the prepreg is winded and cured, and a winding thickness of the prepreg on a striking face is larger than a winding thickness of the prepreg on any other portion. By increasing the weight of the striking face in this way, it is possible to dispose the center of gravity on the striking face and to achieve a golf club having a small moment for easy swing. Further, even though the weight of the head is increased, it is possible to achieve a golf club having a balance that is not different from that of a golf club in the related art. 
         [0011]    By increasing the winding thickness of the prepregs on the head end compared with the winding thickness of the prepregs in the intermediate portion, it is preferably possible to increase the strength on the head end; 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawing which is given by way of illustration only, and thus is not limitative of the present invention and wherein: 
           [0013]      FIG. 1  is a diagram illustrating winding of prepregs. 
           [0014]      FIG. 2A  is a side view of a mandrel, 
           [0015]      FIG. 2B  is a cross-sectional view of prepregs wound on the mandrel, and 
           [0016]      FIG. 2C  is a cross-sectional view of a shaft in a length direction. 
           [0017]      FIGS. 3A and 3B  are perspective views of a golf club and a shaft thereof. 
           [0018]      FIG. 4  is a plan view of a prepreg. 
           [0019]      FIG. 5  is a plan view of prepregs. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Hereinafter, embodiments of the invention will be described with reference to the accompanying drawings. 
         [0021]      FIG. 1  and  FIG. 2  are diagrams illustrating a method of manufacturing a golf club shaft according to an embodiment of the present invention.  FIGS. 2A to 2C  are enlarged views schematically illustrating a mandrel  10  and prepregs wound in a radial direction. 
         [0022]    In the manufacturing method, the mandrel  10  and prepregs  11  to  21  are used. A central axis line of the mandrel  10  is a straight line. The shape of a cross section perpendicular to the central axis line of the mandrel  10  is circular. As shown in  FIG. 2(   a ), the mandrel  10  has a taper in which a head end (head side) is thin and a striking face (grip end) is thick, but may have an equivalent radial portion of which the diameter is partially constant. 
         [0023]    Preferably, after a parting agent is coated on the surface of the mandrel  10 , the prepregs  11  to  21  of a sheet shape are sequentially wound. The prepregs  11  to  21  include a carbon resin and a matrix resin. 
         [0024]    In the present embodiment, in the prepregs  11 ,  14 ,  16 ,  18 ,  19 ,  20  and  21 , fibers are orientated in a straight direction, that is, in a shaft length direction. In the prepregs  15  and  17 , fibers are oriented in a hoop direction, that is, in a shaft circumferential direction. Here, the fibers of the prepreg  19  may be in the hoop direction. In the prepreg  12 , the fibers are oriented in a biased direction of +45° (direction oblique to the shaft length direction), and in the prepreg  13 , the fibers are oriented in a biased direction of −45°. Here, the fibers of the prepreg  12  may be oriented by the angle of −45°, and the fibers of the prepreg  13  may be oriented by the angle of +45°. Further, the biased direction is not limited to 45°, and may have the range of 30° to 60°. 
         [0025]    The prepregs  11  and  14  to  21  have a width to be wound on the outer circumference of the mandrel  10  by one round. The prepregs  12  and  13  have a width to be wound on the outer circumference of the mandrel  10  by a plurality of rounds, for example, 2 to 5 rounds. 
         [0026]    The prepregs  12 ,  13 , and  15  to  19  have a length extending over the entire length of the shaft. The prepregs  11 ,  20  and  21  have a length of 8% to 20% of the entire length of the shaft, and particularly, a length of about 10 to about 15% thereof to be distributed only on the head end of the shaft. By winding the prepregs  11 ,  20  and  21 , the winding thickness of the head end is increased. The prepreg  21  has a triangular shape in which the width becomes large as it goes to the head end, and thus, the vicinity of the head end of the shaft has a cylindrical shape of an approximately uniform diameter. The vicinity of the head end is inserted into a hosel hole of a head. 
         [0027]    The prepreg  14  is distributed only on the striking face, and the length thereof in the shaft length direction is preferably 15% to 45% of the entire length of the shaft, particularly, 20% to 40%, and more particularly 25% to 35%. By selecting the number of the prepregs  14 , the winding thickness of the striking face is increased, as shown in  FIG. 2B . 
         [0028]    It is preferable that the thicknesses of the prepregs  12  and  13  be 0.125 mm or less, and particularly, about 0.05 mm to about 0.1 mm. It is preferable that the thicknesses of the prepregs  15  and  17  be 0.1 mm or less, and particularly, about 0.02 mm to about 0.05 mm. It is preferable that the thicknesses of the prepregs  16 ,  18  and  19  be 0.125 mm or less, and particularly, about 0.05 mm to about 0.1 mm. It is preferable that the thicknesses of the prepreg  14  be 0.05 mm to 2.0 mm, and particularly, about 0.075 mm to about 0.15 mm. It is preferable that the thicknesses of the prepregs  11 ,  20  and  21  be 0.05 mm to 0.2 mm, and particularly, about 0.075 mm to about 0.15 mm. 
         [0029]    It is preferable that the volume fraction of fibers in the respective prepregs  11  to  21  be 60 vol % to 80 vol %, and particularly, about 70 vol % to about 75 vol %. It is preferable to use an epoxy resin or the like as the resin. 
         [0030]    It is preferable that the tensile elasticity of the carbon fibers in the prepregs be 10 ton/mm 2  to 46 ton/mm 2  in the case of the straight direction, and particularly, about 20 ton/mm 2  to about 40 ton/mm 2 . Further, it is preferable that the tensile elasticity thereof be 8 ton/mm 2  to 30 ton/mm 2  (about 78.4 GPa to about 294 GPa) in the case of the hoop direction, and particularly, about 10 ton/mm 2  to about 24 ton/mm 2 . It is preferable that the carbon fibers oriented in the biased direction have a high modulus elasticity of 40 ton/mm 2  (about 392 GPa) or more, for example, 40 ton/mm 2  to 55 ton/mm 2 . 
         [0031]    In a case where the prepregs  11  to  21  are wound on the mandrel  10 , the prepregs  11  to  21  may be wound one by one, or may be wound while pasting a part of the prepregs. For example, the prepregs  15  and  16  may be pasted together, or the prepregs  17  and  18  may be pasted together. An operation of winding the prepregs  11  to  21  on the mandrel  10  may be manually performed, or may be performed by a winding machine (also referred to as a rolling machine). After the prepregs  11  to  21  are wound on the mandrel, a wrapping tape winding process is performed. Although not shown, the wrapping tape is wound in a spiral shape. 
         [0032]    After the winding process, a curing process is performed by heating, and thus, the matrix resin in the prepregs is cured. 
         [0033]    After the curing process, extraction of the mandrel and removal of the wrapping tape are performed, to thereby obtain a cured tubular body (element tube). The opposite ends of the element tube are cut as necessary and are ground, to thereby obtain a golf club shaft  3  (see  FIG. 3B ). Then, a head  2  and a grip  4  are mounted to the golf club shaft  3 , to thereby obtain a golf club  1  (see  FIG. 3A ). 
         [0034]    In the shaft  3 , it is preferable that the thickness of the rearmost end of a striking face  3   c  be 2.5 mm to 1.0 mm, and particularly, 0.6 mm to 0.8 mm. It is preferable that the thickness of the head end of a head end  3   a  is 1.3 mm to 1.8 mm, and particularly, 1.4 mm to 1.7 mm. Further, it is preferable that the average thickness of an intermediate portion  3   b  is 0.4 mm to 0.7 mm, and particularly, about 0.5 mm to about 0.65 mm. It is preferable that the thickness of the rearmost end of the striking face  3   c  be larger than the average thickness of the intermediate portion  3   b  by 0.1 mm to 0.4 mm, and particularly, by 0.125 mm to 0.3 mm. By increasing the thickness of the striking face  3   c  in this way, the weight of the shaft  3  on the striking face is increased. It is preferable that a range L of the striking face  3   c  having a large thickness be 15% to 45%, particularly, 20% to 40%, and more particularly, 25% to 35% of the entire length of the shaft  3  from the striking face of the shaft  3 . 
         [0035]    In the case of a shaft for a wood golf club, the entire length of the shaft is about 1050 mm to about 1220 mm. In the case of the wood golf club shaft, it is preferable that the position of the center of gravity be present in the range of 52% to 57% from the head end of the shaft  3  on the head end. It is preferable that the weight of the shaft be about 40 g to about 50 g. Further, in this case, the outer diameter of a region that ranges from the head end to 250 mm be 8.9 mm to 9.5 mm. It is preferable that a portion between the head end  3   a  and the intermediate portion  3   b  and a boundary portion between the intermediate portion  3   b  and the striking face  3   c  have a taper of about 6.5/1000 to about 7.2/1000. 
         [0036]    In this embodiment, since the thickness of the head end  3   a  is larger than that of the intermediate portion  3   b , the strength of the head end  3   a  is high. 
         [0037]    The layering example of the prepregs in  FIGS. 1  and is an example of the invention, and thus, layering examples other than the example in  FIGS. 1 and 2  maybe used. For example, in  FIG. 1 , a prepreg in which the fibers are oriented in the hoop direction, that is the same as the prepreg  15  (or  17 ), may be disposed between the prepregs  18  and  19  in which the fibers are oriented in the straight direction. Further, in  FIG. 1 , a part of the prepregs in which the fibers are oriented in the hoop direction, for example, the prepreg  17  in  FIG. 1  may be omitted. Further, the number of the prepregs  12  and  13  in which the fibers are oriented in the biased direction may be changed to 4 to 6 in total. In a normal case, it is preferable to layer three to five sheets of prepregs, other than the prepreg  14 , in which the fibers are oriented in the straight direction, one to three sheets of prepregs  14 , two, four or six sheets of prepregs in which the fibers ate oriented in the biased direction, and one to three sheets of prepregs in which the fibers are oriented in the hoop direction. In the present embodiment of the invention, a prepreg  14 A that is large in length in the hoop direction as shown in  FIG. 4  may be used as the prepreg  14 . Further, instead of one sheet of prepreg  14 , as shown in  FIG. 5 , a plurality of sheets of prepregs  14   a ,  14   b  and  14   c  may be used. In this case, the size of the prepreg wound outside may be decreased, as in the prepregs  14   a  to  14   c.    
         [0038]    In the above description, only the carbon fibers are included in the prepregs, but other fibers such as glass fibers, silicon carbide fibers, alumina fibers, aromatic polyamide fibers or boron fibers may be mixed therein.