Abstract:
A putter head includes a head main body and a face insert which is mounted in a face surface of the head main body and formed of viscoelastic body, the face insert having a plurality of slits extending in a direction of toe to heel on a front surface thereof. The face insert is formed of a layered body in which first viscolastic bodies and second viscoelastic bodies having a lower hardness than the first viscoelastic bodies are placed on one another alternately in a direction intersecting the face surface. The slits are formed by eluting the face surface side of the second viscolastic body. The slits are inclined upward in a depth direction from the front face of the face insert to the rear side.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a putter head of a golf club, more particularly to a putter head containing a face insert mounted in a face surface of a head main body thereof. 
       BACKGROUND OF THE INVENTION 
       [0002]    A golf putter is used mainly for hitting a ball mainly on a green to roll the ball toward a cup. JP3087804U describes mounting of the face insert (called “elastic member” in this specification) in the face surface of the putter to soften a feeling of putting a ball. 
         [0003]    JP3087804U intends to provide a putter head capable of enhancing a directional stability of putting. 
         [0004]      FIG. 4  is a sectional view of a putter head of JP3087804U. An elastic member  14  is provided on the front face of a head main body  13  of a head  10  and the elastic member  14  has four lines of slits  16  parallel to each other. The abstract of disclosure of JP3087804U describes as follows. 
         [0005]    A golf ball is hit by a portion provided with the elastic member  14  of the face surface  12 . As a result, the surface of the golf ball  18  pressed by the hitting area enters the elastic member  14  while denting the surface of the elastic member  14  elastically, so that a contact area between the golf ball  18  and the elastic member  14  increases despite a distribution of dimples  26  in a hitting range. Furthermore, the elastic member  14  is provided with four slits  16  parallel to each other in a longitudinal direction of the head  10  and consequently, when the elastic member  14  makes contact with the golf ball  18 , the putter head is deformed mainly perpendicularly to the longitudinal direction of the putter head  10 . As a result, deflection in restoration force, which results from the deformation in the longitudinal direction of the putter head  10 , can be prevented thereby enhancing a directional stability of putting. 
         [0006]    As described in paragraph 0013 to 0017 of JP3087804U, the elastic member  14  is constituted of silicone rubber whose hardness (JIS K6301) is 70 to less than Hs JIS A. The thickness of the elastic member  14  is 1 to 2 mm, the depth of the slit  16  is 1 to 2 mm, and the pitch of the slit  16  is 2 to 4 mm. 
         [0007]    Although, in  FIG. 4 , the slit  16  runs through the elastic member  16  from the front surface to the rear surface, an elastic member proposed by JP3087804U is so constructed that the slit is formed in the shape of a groove, which is formed up to halfway in a thickness direction of the elastic member  16 . 
         [0008]    JP3087804U states nothing about how to form the slit  16 . 
         [0009]    Generally, because silicone rubber is soft, it is extremely difficult to form the slit  16  with high dimensional precision even if it is attempted to form the slit by cutting. 
         [0010]    Even if it is attempted to form the elastic member  14  with the slit  16  by injection molding, a frictional force between a core for use in forming the slit and a slit inner surface of a molded product is so high that it is extremely difficult to remove the core from the molded product. 
         [0011]    The present invention intends to provide a putter head having a face insert provided with slits having excellent dimensional accuracy. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    A putter head of the present invention comprises: a head main body; and a face insert which is mounted in a face surface of the head main body and formed of a viscoelastic body, the face insert having a plurality of slits extending in a direction of toe to heel on a front surface thereof, wherein the face insert is formed of the layered body in which first viscolastic bodies and second viscoelastic bodies having a lower hardness than the first viscoelastic bodies are placed on one another alternately in a direction intersecting the face surface, wherein the slits are formed by eluting the face surface side of the second viscolastic body. 
         [0013]    Preferably, the slit is inclined upward in a depth direction from the front face to the rear face of the face insert. 
         [0014]    According to an aspect of the present invention, an edge between the front face of the face insert and an inside face of the slit is provided with a roundness. That is, the edge between the front face of the face insert and the inside face of the slit has a circular section in the vertical direction. 
         [0015]    According to another aspect of the present invention, the hardness of the first viscoelastic body is greater than the hardness of the second viscoelastic body. 
         [0016]    Preferably, the hardness (Shore hardness) of the first viscoelastic body is D50 to 75 and the hardness of the second viscoelastic body is A20 to 50. 
         [0017]    Preferably, the width of the slit is 0.3 to 0.7 mm and an interval between the slits adjacent to each other is 1.1 to 1.5 mm. 
         [0018]    In the face insert of the putter head of the present invention, the slits are formed by eluting the face surface side of the second viscolastic body from the layered body constituted of the first viscoelastic body and the second viscoelastic body, thereby ensuring an excellent dimensional accuracy of the slits. 
         [0019]    In a case in which the slit is formed to be inclined upward from the front face of the face insert main body to the rear side, the front end side of the first viscoelastic body is deflected downward or backward when the face insert hits a ball. As a result, top spin is easy to apply to the ball, thereby improving the straight advance performance of the ball after it is hit. 
         [0020]    Because the intersection portion between the front face of the face insert and the inside face of the slit is provided with roundness, abrasion of the intersection portion is controlled, thereby improving the durability of the face insert. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1A  is an exploded perspective view of a putter head according to an embodiment of the present invention,  FIG. 1B  is a front view of the putter head, and  FIG. 1C  is a sectional view taken along the line C-C of  FIG. 1B . 
           [0022]      FIG. 2A  is a longitudinal sectional view of a face insert, and  FIG. 2B  is an enlarged longitudinal view of a front surface of the face insert of  FIG. 1A . 
           [0023]      FIG. 3  is a sectional view of a layered body for producing the face insert. 
           [0024]      FIG. 4  is a sectional view of a putter head according to a conventional example. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    The embodiments of the present invention will be described with reference to the accompanying drawings. 
         [0026]      FIGS. 1 to 3  show a putter head  1  of a first embodiment. This putter head  1  is provided with a concave portion  2 H in the front face (face surface) of a head main body  2  and a face insert  3  is disposed within this concave portion  2 H. According to this embodiment, the head main body  2  is made of metal such as aluminum alloy, titanium alloy, copper alloy, and stainless steel. The face insert  3  is formed of viscoelastic body and has several lines of slits  5  on its front face. 
         [0027]    The concave portion  2 H and the face insert  3  are of a substantially rectangular shape which is horizontally long. The depth of the concave portion  2 H is entirely even and the thickness of the face insert  3  is entirely even. However, the face insert may be provided partly with a deep portion or a thick portion, or conversely may be provided partly with a shallow portion or a thin portion. 
         [0028]    The lateral and vertical widths of the face insert  3  are slightly smaller than those of the concave portion  2 H and there is a slight gap  6  between top, bottom, right and left side faces  3 S of the face insert  3  and a peripheral face  2 S of the concave portion  2 H. Preferably, the width of this gap  6  is 0.3 to 1.5 mm, particularly 0.4 to 1.0 mm. 
         [0029]    As regards the size of the face insert  3 , its vertical width is preferred to be 16 to 30 mm, particularly 18 to 25 mm, its lateral width is preferred to be 50 to 150 mm, particularly 70 to 100 mm, and its thickness is preferred to be 2 to 10 mm, particularly 3 to 8 mm. However, they are not limited to these values. 
         [0030]    In this embodiment, the respective slits are provided in multiple stages vertically such that they are spaced at a specific interval. The slits  5  are positioned on the front face (face surface) of the face insert  3 . The slits  5  are formed so as to be positioned higher toward their rear ends. When the front face of the face insert  3  is positioned perpendicularly to the ground, an inclination angle θ of the slit is preferred to be 20 to 70° and more preferred to be 30 to 60°. 
         [0031]    The interval between the slits  5  is preferred to be 1.1 to 1.5 mm, and more preferred to be 1.2 to 1.4 mm. The width (vertical width) t of the slit  5  is preferred to be 0.3 to 0.7 mm, and more preferred to be 0.4 to 0.6 mm. 
         [0032]    The face insert  3  is disposed within the concave portion  2 H such that its left side face in  FIG. 2A  serves as a front surface of the putter head and an opposite surface is bonded to a deep wall surface of the concave portion  2 H with adhesive. As the adhesive, epoxy base adhesive, rubber base adhesive or double-sided adhesive tape is preferable; however, it is not limited to these materials. 
         [0033]    To manufacture the face insert  3 , first viscoelastic bodies  7  and second viscoelastic bodies  8  are placed on one another alternately as shown in  FIG. 3  to form a layered body  3 ′ and then, the second viscoelastic body  8  is eluted through the front face of the layered body  3 ′. 
         [0034]    The hardness (Shore hardness based on JIS K 6253, ASTM D 2240) of the first viscoelastic body  7  is preferred to be D50 to 75, and is more preferred to be D55 to 70, and the hardness of the second viscoelastic body  8  is preferred to be A20 to 50. The second viscolastic body  8  is softer than the first viscoelastic body  7 . 
         [0035]    The thickness of the second viscolastic body  8  agrees with the vertical width t of the slit  5 . 
         [0036]    As the viscoelastic material for constructing the face insert  3 , thermoplastic elastomer or soft synthetic resin is used. These materials may be of foamed material. 
         [0037]    As a material for the first viscolastic body  7 , specifically, polycarbonate resin, ABS resin, polyester resin, polyolefin resin, polyvinyl chloride resin, polyamide resin and the like are available. As a material for the second viscoelastic body  8 , olefin or styrene elastomer, ester elastomer, amide elastomer, silicon resin and the like are available. However, they are not limited to these materials. Although it is preferred to bond the first viscelastic body  7  with the second viscoelastic body  8  by pressing with heat, the bonding method is not limited to this one. 
         [0038]    To elute the second viscoelatic body  8 , preferably, the rear face and the side faces of the layered body  3 ′ are sealed with a film or the like and the layered body  3 ′ is immersed in strong alkaline aqueous solution. By heating the strong alkaline aqueous solution, the elution rate of the second viscoelastic body  8  is increased. 
         [0039]    Due to the elution treatment, an intersection portion between the front face of the face insert  3  and the slit  5  comes to have a roundness. That is, in  FIG. 2B  which is an enlarged longitudinal sectional view taken along a back and forth direction of the face insert  3 , an intersection portion  7   a  becomes convexly curved in its section. 
         [0040]    The intersection portion having such a roundness prevents abrasion of the intersection portion compared to an intersection having a sharp edge thereby improving the durability of the face insert  3 . 
         [0041]    Due to the aforementioned elution treatment, a face opposing the bottom of the slit  5  of the second viscoelastic body  8  becomes concavely curved. 
         [0042]    By implementing the elution treatment upon the layered body  3 ′, the slit  5  having an excellent dimensional accuracy is produced. A head  1  equipped with the slits  5  having an excellent dimensional accuracy can hit a ball easily in a target direction. 
         [0043]    In this embodiment, the slit  5  is inclined upward toward its rear end. As a result, when the head  1  hits a ball, the front face of the face insert  3  is deformed downward and obliquely backward so as to facilitate application of top spin and improve a straight advance performance of the hit ball. 
         [0044]    Although, in the above embodiment, the slit  5  is inclined upward toward the rear end, the slit  5  may be formed horizontal toward the rear end or may be inclined downward toward the rear end. When the slit  5  is inclined downward toward the rear end, the top spin of the ball when it is hit is decreased, so that back spin of the ball becomes easy to apply. Thus, on a little rough green or a slippery green, a player can adjust his or her feeling toward a distance more easily because the ball comes to roll badly. That is, generally, after a hit with a putter, the ball moves without any rotation or by sliding at few rotations on the green just after it leaves the face surface of the putter. After a while, due to a friction between the ball and the green surface, the ball rolls without being slipped on the green (a peripheral velocity of the ball becomes equal to a moving velocity of the ball). If a force in the direction of top spin applied to the ball is decreased or a force in the direction of back spin when a hit with the putter head is applied to the ball, a sliding moving distance without any rotation or at few rotations just after the ball is hit increases. On a rough green, an influence on the ball of the green surface during a sliding move without any rotation or at few rotations just after the ball is hit decreases, so that a total sliding distance until the ball is stopped is equal to or about equal to a case of a ordinary green. Further, on a green allowing excellent rolling (more specifically, short-cut green or hard-tightened green with a roller or the like), the roll of the ball just after a hit is suppressed due to weakened top spin or generated back spin. Consequently, the total rolling distance until the ball is stopped becomes equal to or about equal to a case of an ordinary green. As a result, the putter head of the present invention enables a player to adjust his or her feeling toward a distance when he or she plays on a little rough green or a green allowing excellent rolling, so that the ball rolls just over an intended distance. 
         [0045]    In  FIG. 1 , the gap  6  is formed around the face insert  4 . The gap may be filled with viscoelastic material such as rubber, elastomer, synthetic resin. Alternatively, the face insert  4  may be formed so as to fit to the concave portion  2 H without the gap  6 .