Abstract:
A diamond-like carbon (DLC) coated golf club head primarily for reduction of friction between the hitting surface and the golf ball at impact. The DLC coating comes in two varieties including dehydrogenated DLC or hydrogenated DLC and is thinly applied between about 0.1 and 10 μm. The diamond particle size of individual diamond-like carbon molecules or crystals can be less than 0.1 μm, and preferably less than 1 nanometer. The DLC coating may be bonded to the golf club head or hitting surface using cathodic arc method or other applicable methods at temperatures of less than 200° C.

Description:
[0001]    The present application is a continuation-in-part application based on a U.S. patent application filed on Apr. 7, 1999, and having the Ser. No. 09/287,241. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to improvements in the performance of a golf club, especially golf clubs used for distance. More specifically, the invention relates to the coating of the face or hitting surface of a golf club head with diamond-like carbon (DLC) to drastically reduce the frictional coefficient on the face of the golf club head, thereby increasing golf ball distance and accuracy.  
         BACKGROUND OF THE INVENTION  
         [0003]    Golf is a very popular sport among people of all ages. As such, the golf equipment industry is constantly seeking to improve the design of golf equipment, especially golf clubs, to meet the demands of many golfers trying to improve their game or obtain a competitive edge over fellow golfers. There have been numerous attempts over the years to improve the performance of golf clubs and indeed, this continues today.  
           [0004]    Essentially, the game of golf can be broken down into two major skills, the long game and the short game. The long game involves skills such as “driving” a golf ball long distances from the tee box and/or hitting a golf ball long distances from the fairway. The short game involves skills such as “pitching” a golf ball from a location near the putting green and “putting” the golf ball from a spot on the green into a hole. Since the skills utilized in the long game and the short game are different, club designs vary accordingly, i.e., a putter is designed differently than a driver.  
           [0005]    When considering how one might improve the performance of a golf club, there are essentially two major variables that should be considered. First, the properties of the shaft may be considered when seeking to increase performance of a golf club. For example, golf club shafts have traditionally been designed using metal materials. However, there has been a recent trend toward the use of graphite shafts. Additionally, the shaft length and/or the angle relationship between the shaft and the golf club head may be modified to alter performance. These latter two alterations are typically made when a person wishes to have their clubs customized.  
           [0006]    Second, and more applicable to the present invention, the design of the golf club head itself effects the performance of a given club. Particularly when using clubs such as drivers and other long game clubs, the distance and direction that a golf ball travels is critical. As a result, many different geometric shapes and materials have been tried in order to vary the design of golf club heads in hope of achieving high performance, i.e., increased distance and improved accuracy.  
           [0007]    Regarding geometric shape of golf club heads, many different shapes have been manufactured. For example, there has been a recent trend toward the design of driver heads with increased volume. Additionally, clubs commonly called “irons” have evolved from having solid golf club heads to golf club heads having perimeter weighting. Perimeter weighted golf club heads have many advantages over older clubs including increased distance and increased control of a golf shot.  
           [0008]    Regarding the material used to construct golf club heads, many materials have been used including hard wood (e.g., persimmon), metal (e.g., steel, cast iron, aluminum, copper, titanium), graphite (e.g., Thunder Head wood from Spalding®), plastic (e.g., Odyssey as described in U.S. Pat. No. 5,342,812 issued to G. Rennie) or other materials (e.g., metal matrix composite as described in U.S. Pat. No. 8,342,812 issued to P. Niskanen et. al.). Presently, drivers are primarily made from titanium or iron.  
           [0009]    An important part of a golf club is the face of the club head. The face of the club head can best be described as the hitting spot or surface. This is where the golf club interfaces with the golf ball during a golf swing. When a golf ball is struck, the material at the contact point or hitting surface will deform elastically and then rebound immediately. Though this cannot be entirely prevented, reduction of this deformation is desirable so that the energy of the swing can be more effectively transferred to the golf ball. As a result, many attempts have been made to improve the rigidity of the material used in golf club heads. This is particularly true with regard to the face or hitting surface of the golf club head.  
           [0010]    When considering materials with high rigidity, one candidate to consider is diamond. In U.S. Pat. Nos. 4,951,953 and 5,029,865 issuing to D. Kim, a ball striking surface of a golf club head is disclosed having diamond coating for increased surface rigidity. The particles can be embedded using an electroless “composite diamond coating” technique. Specifically, the patent claims the use of a composite comprising a diamond component and a metal or metal alloy such as a nickel matrix. The entire thickness of the composite coating can be from 1 to 2 mils. Alternatively, in U.S. Pat. No. 5,620,382 issuing to H. Sam Cho, et al., the use of a polycrystalline diamond or cubic boron nitride insert is disclosed. The insert is comprised of a surface layer (bonded diamond-diamond or CBN-CBN crystals) and a hard or rigid support layer. The insert is then inserted, i.e., cemented in a metal or ceramic matrix, into a cavity on the golf club head.  
           [0011]    Though diamond has the highest modulus of rigidity, there are some basic problems with the use of diamond or diamond powder in general. First, because the hitting surface is so hard, there is very little deformation of the club head creating a greater impact force. As a result, the golf ball, which is much softer than the club, experiences more ovalation than is typically experienced. Thus, the contact area between the hitting surface of the club head and the golf ball is increased momentarily. Because the contact area is increased, the frictional force between the hitting surface of the club head and the golf ball is also increased. In other words, because there is more contact between the golf ball and the hitting surface, there is more friction. Moreover, there are additional problems when a diamond-metal composite is used in that diamond is much harder than metal. Therefore, when a diamond-metal composite is polished, diamond grains, being more rigid than metal, will not wear down at the same rate as metal thereby causing the diamond grains or particles to protrude higher than the metal matrix after polishing. This unevenness will further increase the frictional force between the hitting surface of the club head and the golf ball.  
           [0012]    Higher frictional force between the hitting surface and the golf ball is generally undesirable because unless the golf ball is perfectly hit, there is a greater likelihood of “hooking” or “slicing” a given shot. “Hook” and “slice” are golf terms used to describe the direction a golf ball travels when the path of flight is not linear, but arcuate in a direction toward or away from the golfer respectively. This occurs as the golf ball spins on a more vertical axis. Therefore, the higher the spin rate, the more curvature, i.e., “hook” or “slice”, the flying ball will experience. These type of shots are normally undesirable for two reasons. First, the distance that the golf ball travels is reduced because energy is wasted on angular momentum, i.e., spin, and heat generated from the increased friction. Both of these energies reduce the desired forward momentum. Second, since the desired direction is compromised, the next shot becomes more difficult. Additionally, though back spin is desirable for some shots, even back spin will diminish the distance of a golf shot.  
           [0013]    With regard to diamond hitting surfaces of club heads, there are also economic concerns. The preparation of diamond-metal composite (PCD) requires somewhat difficult and expensive modifications of a golf club. First, in order to insert a composite into a club head, the hitting surface must be machined to create a cavity or void for insertion of the diamond-metal composite. Additionally, diamond-metal composite is expensive and the process of preparation is tedious making this option unaffordable to most golfers. Moreover, the hitting surface of a club head containing a diamond-metal composite requires frequent polishing and/or grinding. This additional work is time consuming and difficult to accomplish due to the presence of diamond.  
           [0014]    In addition to issues surrounding rigidity, attempts have also been made to reduce the friction on golf club heads. For example, U.S. Pat. No. 5,885,171 issuing to Sharpe on Mar. 23, 1999 discloses a system for altering the friction coefficient between a golf club face and a golf ball. This patent teaches that a liquid coating, such as a lubricant, can be applied to the face or hitting surface of a golf club to lower the frictional coefficient. Though the goal of lowering the frictional coefficient is worthy, there are several disadvantages to the system disclosed in U.S. Pat. No. 5,885,171. First, applying a liquid lubricant is messy and if the golfer is not careful, the lubricant can get on the golfer&#39;s hands causing slippage on subsequent swings. Second, some lubricant will surely pass from the golf club head to the ball causing the ball to fly through the air unevenly. Third, many golf shots necessarily require that the golf club strike the substrate or earth prior to hitting the golf ball. As such, some lubricant will be wiped from the club prior to striking the ball. Finally, it is inconvenient to be required to apply a liquid lubricant to a golf club prior to a golf shot, and further, be required to remove the same lubricant from the golf club head when completing a golf round.  
           [0015]    A second example of a patent that discusses the reduction of friction on a golf club head can be found in U.S. Pat. No. 5,531,444 issuing to Buettner on Jul. 2, 1996. In that patent, a coating of titanium nitride as applied to a golf club head is disclosed. The patent states that the coating of titanium nitride provides a “very hard, tough, and low-friction coating.” However, to coat a metal golf club head with titanium nitride, high temperatures must be used. The patent further states that precautions must be taken to prevent the golf club head from deforming or distorting, i.e., “the bore in the club head hozzle tends to distort.” As such, the patent claims a method to prevent distortion of the club head hozzle. Though the inventor has succeeded at preventing distortion of the “club head nozzle,” the development of a superior coating is desirable that has a lower friction coefficient and does not require high temperatures to apply, thereby preventing distortion and/or weakening the golf club head.  
           [0016]    It has been recognized that it would be desirable to provide a golf club head that is relatively inexpensive to manufacture, is reasonably rigid at the hitting surface, does not distort when a coating is applied, and drastically reduces the frictional force between the hitting surface and the golf ball on impact.  
         SUMMARY OF THE PRESENT INVENTION  
         [0017]    The present invention pertains primarily to an improved golf club, more particularly, an improved golf club head. The golf club head of the present invention is comprised of a body having a hitting surface and a coating of diamond-like carbon (DILC). The diamond-like carbon (DLC) is used to coat a golf club head, particularly the hitting surface but including the lower surface, at a thickness of between about 0.1 and 10 μm. Additionally, the diamond-like carbon (DLC) of the coating can have a grain size or diamond molecule size of less than 0.1 μm. Larger diamond grain sizes can increase the friction between the golf club head hitting surface and the ball to less desirable levels compared to those of the present invention. Preferably, the present invention is intended to coat iron and/or titanium golf club heads, though golf club heads made from different materials or composites can also be used.  
           [0018]    Regarding the diamond-like carbon coating, there are essentially two types that may be used in the present invention. First, diamond-like carbon (DLC) containing less than 10% (by atoms) of hydrogen may be used (hereinafter “dehydrogenated DLC”). If dehydrogenated DLC is used, the percentage of diamond in the diamond-like carbon (DLC) will be from 50% to 95% by atoms. A more preferred percentage range of diamond is from 80% to 95% by atoms. Second, diamond-like carbon (DLC) containing at least 10% by atoms of hydrogen may be used (hereinafter, “hydrogenated DLC”). If hydrogenated DLC is used, the percentage of diamond in the diamond-like carbon will be from 20% to 60%. A more preferred percentage range of diamond is from 30% to 60% by atoms. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    In the accompanying drawings which illustrate embodiments of the invention:  
         [0020]    [0020]FIG. 1 is a perspective view of a golf club head indicating the preferred locations for coating; and  
         [0021]    [0021]FIG. 2 is a cross-sectional view of a golf club head coated in various areas with a diamond-like carbon (DLC) 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    Before the present invention is disclosed and described, it is to be understood that this invention is not limited to the particular process steps and materials disclosed herein as such process steps and materials may vary to some degree. It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only and is not intended to be limiting as the scope of the present invention will be limited only by the appended claims and equivalents thereof.  
         [0023]    It must be noted that, as used in this specification and the appended claims, singular forms of “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise.  
         [0024]    In the accompanying drawings, FIG. 1 shows a perspective view of a golf club head  10  having a diamond-like carbon (DLC) coated hitting surface  12 . Additionally, a diamond-like carbon (DLC) coated lower surface  14  is shown. Turning to FIG. 2, a cross-sectional view of the golf club head  10  is shown. Both a diamond-like carbon (DLC) coated hitting surface  12  and a diamond-like carbon (DLC) coated lower surface  14  are shown as adhered to a body  16  of the golf club head  10 .  
         [0025]    With these figures in mind, the present invention is drawn to a golf club head comprising a body having a hitting surface wherein the hitting surface is coated with from 0.1 μm and 10 μm of diamond-like carbon (DLC) coating, and wherein the diamond-like carbon (DLC) of the coating has a grain size or molecule size of less than 0.1 μm. In one embodiment, a lower surface is also coated with from 0.1 μm and 10 μm of diamond-like carbon (DLC) coating. There, the diamond-like carbon (DLC) of the coating can also have a grain size of less than 0.1 μm. Thus, practically speaking, when diamond is present, the lower end of the particle size (with respect to both the hitting surface and the bottom coating) can be as small as a single tetrahedral carbon molecule dimension. In one embodiment where the bottom surface is coated, the hitting surface coating and the bottom surface coating can be a single continuous coating. In this embodiment, the rest of the golf club or golf club head need not be coated likewise, though such coating is not prohibited. In another embodiment, the diamond-like carbon (DLC) coating can extend from the hitting surface to another part of the head.  
         [0026]    Though the grain size or molecule size can be as large as less than 0.1 μm, it is preferred that the diamond-like carbon (DLC) of the coating have a grain size of less than about 1 nanometer. In a more specific embodiment, the diamond-like carbon (DLC) grain size can be amorphous, also known as distorted tetrahedral carbon.  
         [0027]    With the present invention, the coating can be applied to a metal golf club head. Though other composites can also be used, metal golf club heads such as iron or titanium are preferred for this invention. Further, though the entire golf club head can be coated with diamond-like carbon (DLC), the hitting surface must be coated with diamond-like carbon (DLC) for the invention to have the desired effect with respect-to the golf ball. However, it may be desirable to coat other surfaces, such as the bottom surface, to reduce friction as the golf club head brushes the grass, dirt or other substrates.  
         [0028]    Generally, diamond-like carbon (DLC) is essentially a composite of diamond, graphite or non-diamond carbon, and/or a polymer. More specifically, diamond-like carbon (DLC) is a composite material that can comprise three end members. First, diamond which is carbon bound together with sp 3  bonds (tetrahedral) can be present. Second, graphite which is carbon bound together with sp 2  bonds (triagonal) can be present. Third, a polymer such as a hydrocarbon plastic can be present as well. Thus, the carbon portion is substantially supplied by graphite and/or diamond, and the hydrogen is substantially provided by the polymer. In one embodiment, the diamond-like carbon (DLC) coating can comprise diamond, graphite, and a hydrocarbon plastic. In an alternative embodiment, the diamond-like carbon (DLC) coating can comprise diamond and a hydrocarbon plastic. In yet another embodiment, the diamond-like carbon (DLC) coating comprises randomly assembled diamond carbon atoms and graphite carbon atoms, thus forming an amorphous coating structure.  
         [0029]    For practical purposes, diamond-like carbon (DLC) can be divided into two major categories. The first category includes those diamond-like carbons (DLC) that contain at least 10% hydrogen by atom, i.e., hydrogenated DLC having more polymer present. The second category are those diamond-like carbons (DLC) that contain less than about 10% hydrogen by atom, i.e., dehydrogenated DLC having less hydrogen present. The hydrogenated DLC contains from 20% to 60% diamond by atom whereas dehydrogenated DLC contains from 50% to 95% diamond by atom.  
         [0030]    As stated, carbon may form either sp 2  bonds or sp 3  bonds. sp 2  bonds indicate the presence of graphite and sp 3  bonds indicate the presence of diamond. The ratio of these two types of bonds may be measured by Raman spectroscopy which is well known in the art. This is significant because the number of sp 3  bonds (diamond) determines the closeness of diamond-like carbon (DLC) to diamond. Thus, hydrogenated DLC is less rigid or hard than dehydrogenated DLC. Though this is the case, all diamond-like carbons (DLC) have a very low frictional coefficient. However, the frictional coefficient of hydrogenated DLC increases in the presence of water or moisture. Conversely, dehydrogenated DLC is less affected by moisture. Therefore, wet conditions from rain or humidity will not adversely affect the performance of golf club heads coated with dehydrogenated DLC. As a result, dehydrogenated DLC is preferred for the present invention, although hydrogenated DLC can also be used.  
         [0031]    To utilize the present invention, at least one layer of diamond-like carbon (DLC) can be coated on the face or hitting surface of the golf club head. As mentioned, other surfaces can also be coated as needed, e.g., the lower or bottom surface of the golf club head may be coated so that the club head brushes the substrate with reduced friction whereas the upper or top surface need not be coated. Additionally, when applying a layer of diamond-like coating (DLC) to the golf club head, the coating can be deposited directly on the desired surface, e.g., the hitting surface and/or the bottom surface. Therefore, it is not necessary to form a cavity or otherwise alter the shape or texture of the golf club head as is required by some of the prior art.  
         [0032]    The coating of metal substrates with diamond-like carbon (DLC) is not a new concept. Specifically, industry has deposited diamond-like carbon (DLC) onto various materials using primarily physical vapor deposition (PVD). This method energizes carbon atoms at low temperatures by physical means. Physical vapor deposition (PVD) is contrasted to chemical vapor deposition (CVD) which energizes carbon atoms by heating them to a high temperature, i.e. above 600° C. Due to the high temperatures required for CVD, PVD is the method of applying diamond-like carbon (DLC) that is preferred. Specifically, PVD methods known in the art include techniques such as sputtering, ion beam deposition, and cathodic arc (though cathodic arc is a more preferred deposition method for the present invention). However, the mentioning of these methods is not intended to limit the invention as other methods used for coating golf club heads with diamond-like carbon (DLC) are possible.  
         [0033]    One reason that the use of diamond-like carbon (DLC) on the hitting surface of a golf club head is desirable, especially with respect to long game golf clubs, is that diamond-like carbon (DLC) has a very low frictional coefficient, i.e., 0.1 or less. This low frictional coefficient is comparable to teflon or other lubricants. Low friction between the hitting surface of a golf club head and the golf ball reduces heat and spin or angular momentum that a golf ball normally experiences after impact. Therefore, more forward or directional momentum is transferred from the golf club to the golf ball. In other words, the force behind a golf club swing is not wasted on angular momentum or generated heat.  
         [0034]    Another advantage of the present invention is that to obtain a low frictional coefficient, the user is not required the use of a liquid lubricant as discussed in U.S. Pat. No. 5,885,171. The use of a liquid lubricant can be messy and if the golfer is not careful, the lubricant can get on the golfer&#39;s hands causing slippage on subsequent golf swings. Further, since the lubricant is not integrated into the golf club head, some lubricant will pass from the golf club head to the ball. This will cause the ball to fly unevenly or asymmetrically. The present invention provides a golf club head having a low friction coefficient (0.1 or less) on the hitting surface without the disadvantages associated with the use of lubricants.  
         [0035]    Still another advantage of the present invention is that the diamond-like carbon (DLC) can be deposited on the golf club head or hitting surface at a relatively low temperature, i.e., less than 200° C. This is significant because the properties of the base metal, i.e., substance that the golf club head is made of, will not be overheated causing alterations to the dimension or properties of the golf club head. Therefore, applying the diamond-like carbon (DLC) to a titanium or iron golf club head will not adversely affect the shape, relative strength or hardness of the golf club head. Further, the present invention addresses the issues presented in the previous discussion of U.S. Pat. No. 5,531,444 by providing a coating (DLC) that can be applied at a relatively low temperature. As such, the bore in the golf club head hozzle will not distort during the coating process. Additionally, since diamond-like carbon (DLC) is a relatively smooth substance, polishing of the respective golf club heads is minimized if not eliminated where the diamond-like carbon (DLC) has been applied.  
       EXAMPLE  
       [0036]    50 titanium drivers were coated with dehydrogenated DLC using the cathodic arc method. The deposited amorphous or distorted tetrahedral diamond was applied at a thickness of about 3 micrometers. The clubs, having diamond-like carbon (DLC) coated heads, were used by many golfers. Most felt that their golf performance, in particular, their driving distance (due in part to lower degree of hook and slice) had noticeably improved when using diamond-like carbon (DLC) coated golf club heads.  
         [0037]    While the invention has been described with reference to certain preferred embodiments, those skilled in the art will appreciate that various modifications, changes, omissions and substitutions can be made without departing from the spirit of the invention. It is intended, therefore, that the invention be limited only by the scope of the following claims.