Patent Publication Number: US-8529375-B2

Title: Golf ball having increased moment of inertia

Description:
BACKGROUND 
     The present invention relates generally to a golf ball, and a method of manufacturing the golf ball. In particular, a cover layer on the golf ball includes coated areas such that the golf achieves an increased moment of inertia. 
     The game of golf is an increasingly popular sport at both the amateur and professional levels. A wide range of technologies related to the manufacture and design of golf balls are known in the art. Such technologies have resulted in golf balls with a variety of play characteristics. For example, different golf balls are manufactured and marketed to players having different golfing abilities, such as different swing speeds. 
     Accordingly, a golfer may use different golf balls having different play characteristics depending on the golfer&#39;s preferences. For example, different dimple patterns may affect the aerodynamic properties of the golf ball during flight, a difference in the cover hardness may affect the rate of backspin, or a difference in the moment of inertia may also affect the rate of backspin. With regard to the moment of inertia in particular, a golfer may choose to use a golf ball having a higher moment of inertia or a lower moment of inertia. A higher moment of inertia will generally result in a lower rate of spin by the golf ball during flight after being struck by a golf club face, while a lower moment of inertia will generally result in a higher rate of spin by the golf ball. Higher rates of spin are generally associated with better controllability, while lower rates of spin are generally associated with increased distance off the tee. 
     A wide range of golf balls having a variety of moment of inertia characteristics are known in the art. Generally, the moment of inertia of a golf ball is determined by the composition and physical arrangement of the various layers making up the golf ball. Accordingly, a number of different golf ball materials are mixed and matched in various combinations and arrangements to create golf balls having different moments of inertia. 
     However, designing golf balls to achieve desired moment of inertia characteristics suffers from at least several difficulties. Known golf balls generally use heavy additives interspersed in a polymer matrix comprising one or more outer layers of the golf ball, such that the heavy additive adds weight to an outer radius of the golf ball, in order to increase the golf ball&#39;s moment of inertia. However, generally, the construction of known golf balls requires that a wide range of design variables such as layer arrangement, materials used in each layer, and layer thickness be balanced against each other. Changes to any of these variables may therefore achieve a desired moment of inertia only at the expense of other play characteristics. Additionally, materials costs and design costs associated with known golf ball constructions may unduly increase the cost of the golf ball to the end consumer. 
     Therefore, there is a need in the art for a system and method that addresses the shortcomings of the prior art discussed above. 
     SUMMARY 
     In one aspect, this disclosure provides a golf ball comprising: a core having a first density; and a cover layer substantially surrounding the core, the cover layer having multiple dimples and at least one land area separating the dimples; the dimples being arranged on the cover layer in a first pattern; the at least one land area being arranged on the cover layer in a second pattern, the first pattern and the second pattern being non-overlapping patterns; wherein the cover layer is coated with a coating material such that the coating material at least partially overlaps one of the first pattern and the second pattern but substantially does not overlap the other of the first pattern and the second pattern; and wherein the coating material has a second density, the second density being higher than the first density, such that the presence of the coating material increases the moment of inertia of the golf ball. 
     In another aspect, this disclosure provides a method of manufacturing a golf ball, the method comprising the steps of: (1) receiving a golf ball, the golf ball including a core having a first density and a cover layer substantially surrounding the core, the cover layer having a plurality of dimples and at least one land area separating adjacent dimples, the plurality of dimples being arranged on the cover layer in a first pattern, the at least one land area being arranged on the cover layer in a second pattern, the first pattern and the second pattern being non-overlapping patterns; (2) coating the cover layer with a coating material over at least a portion of at least one of the first pattern and the second pattern, the coating material having a second density, the second density being greater than the first density; and, if necessary (3) selectively removing the coating material from the cover layer; whereby the coating material overlaps at least a portion of one of the first pattern and the second pattern but substantially does not overlap the other of the first pattern and the second pattern, and the presence of the coating material increases the moment of inertia of the golf ball. 
     Other systems, methods, features and advantages of the invention will be, or will become, apparent to one of ordinary skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description and this summary, be within the scope of the invention, and be protected by the following claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. 
         FIG. 1  shows an exemplary golf ball before and after selective coating; 
         FIG. 2  shows a cross section of the golf ball shown in  FIG. 1 , before and after the selective coating; 
         FIG. 3  shows an alternative embodiment of a golf ball, before and after selective coating; 
         FIG. 4  shows a cross section of the golf ball shown in  FIG. 3 , before and after the selective coating; 
         FIG. 5  shows a cross section of a portion of a golf ball cover layer, in further detail; 
         FIG. 6  shows a close-up cross section of a portion of a golf ball cover layer, after a part of a selective coating has been removed; 
         FIG. 7  shows a second embodiment of a cross section of a portion of a golf ball cover layer, in further detail; 
         FIG. 8  shows a second embodiment of a close-up cross section of a portion of a golf ball cover layer, after a part of a selective coating has been removed; 
         FIG. 9  is a flowchart detailing a method of manufacturing a golf ball, including optional steps; and 
         FIG. 10  shows a golfer hitting a golf ball, and a comparison of the play characteristics of two golf balls. 
     
    
    
     DETAILED DESCRIPTION 
     Generally, the present disclosure relates to a golf ball having an increased moment of inertia. The increased moment of inertia is achieved by coating a dense material onto the cover layer in a selected pattern. The pattern may correspond to the plurality of dimples, or the pattern may correspond to at least one land area separating at least two dimples. Coating the dense material in a selected pattern increases the golf ball&#39;s moment of inertia while also affording the golf ball other advantageous physical properties, such as a desirable hardness pattern. In one embodiment, coating the dense material in a pattern corresponding to at least one land area separating at least two dimples results in an increased moment of inertia while using minimal dense material due to the dense material being added at the farthest radial distance from the golf ball&#39;s center of gravity. 
     This disclosure further relates to methods of manufacturing such a golf ball. 
     The moment of inertia of a body is a measure of an object&#39;s resistance to changes in its rotation rate. Generally, when a body having a high moment of inertia is imparted with a certain rotational energy, the body will rotate at a rate that is slower than the rate at which a body having a low moment of inertia will rotate when imparted with the same amount of rotational energy. The moment of inertia of a spinning body is generally defined as the integral of r 2 *dm, where r is the radial distance to the axis of rotation and dm is the differential of the mass at that radius r. Moment of inertia has units of mass times distance squared, for example in SI units: kg*m 2 . The moment of inertia of a uniform solid sphere is given by the equation (2/5)*mass*radius 2 . However, a golf ball is not uniform, but instead varies in density among its several layers. The present disclosure changes the rotational performance characteristics of a golf ball by coating a dense material on an outermost layer of the golf ball in a selected pattern. 
       FIG. 1  shows an exemplary golf ball in accordance with this disclosure. Golf ball  100  is made up of a cover layer having thereon a plurality of dimples  104  and at least one land area  106 . Golf ball  100  may generally be any type of golf ball having a core and a cover layer substantially surrounding the core. For example, golf ball  100  may be of a two-piece construction, having only a core and a cover layer, or golf ball  100  may have one or more intermediate layers located between the core and the cover layer. Except as otherwise herein discussed, each layer of golf ball  100  may be formed of any material or construction as is generally known in the art of golf ball manufacturing. For example, various layers of golf ball  100  may be comprised of rubber, rubber composites, thermoplastic polyurethane, highly-neutralized polymers, ionomers, and other polymer materials as are known in the art of golf ball manufacturing. 
     The plurality of dimples  104  may generally be arranged on the cover layer in a first pattern. The first pattern may generally be any dimple-packing pattern, as may be known in the art of golf balls. Dimples  104  may generally be of any shape, such as circular, triangular, or multi-sided. Dimples  104  may be of uniform shape and size, or the dimple pattern may be made up of two or more different types of dimples having (for example) different sizes or different shapes. At least one land area  106  is a part of the cover layer that separates at least two dimples  104  and that is not indented or otherwise part of a dimple. Generally, land area  106  is the “ridge” or “fret” between adjoining dimples  104 . Golf ball  100  may include one continuous land area  106  across the entire cover layer, as is shown in  FIG. 1 , or a plurality of separate land areas between the plurality of dimples  104 . At least one land area is arranged on the cover layer in a second pattern. The first pattern (corresponding to the dimples) and the second pattern (corresponding to the land between the dimples) are different, non-overlapping patterns. 
     In the embodiment shown in  FIG. 1 , golf ball  100  undergoes selective coating so as to be changed into golf ball  130 . The selective coating process itself is discussed in greater detail below. By the selective coating process, a coating material  108  is selectively applied on the first pattern (corresponding to the dimples  104 ). Although  FIG. 6  shows the entirety of the first pattern (i.e., all of the dimples) being coated with coating material  108 , coating material  108  may alternatively coat only a portion of the first pattern. Generally, in this embodiment, coating material  108  may overlap at least a portion of the first pattern, but does not substantially overlap the second pattern. 
       FIG. 2  shows a cross-sectional view of the dimples  104  and land areas  106  shown in  FIG. 1 . In  FIG. 1 , coating material  108  is coated on top of each of the dimples  104 , forming a thin layer of coating material  108  on a cover layer  102 . Generally, cover layer  102  substantially surrounds a core  202 , and includes the dimples  104  and land areas  106  thereon. Although core  202  is shown to be in direct contact with cover layer  102  in  FIG. 2 , the golf ball  100  or  130  may include one or more intermediate layers between core  202  and cover layer  102  as may be desired and as are known in the art of golf ball construction. 
     The thickness of coating material  108  may generally be any thickness that fits within a dimple. Coating material  108  should generally not be so thick as to significantly affect the aerodynamics of the golf ball, however coating material  108  may be applied in such a way as to achieve a desired dimple depth configuration. In certain embodiments, cover layer  102  may have a thickness of about 2 mm or less. A clear coating layer (not shown) on top of cover layer  102  may generally have a thickness of about 20 microns. Accordingly, in these embodiments, coating material  108  may have a thickness that is, for example, on the order of about 20 microns or less. Generally, coating material  108  may have a thickness of about 1 micron to about 20 microns (about 0.001 mm to about 0.02 mm), inclusive and taking into account manufacturing tolerances. 
       FIG. 3  shows a second embodiment, wherein land areas  106  of golf ball  100  are coated with a coating material  110  so as to produce golf ball  140 . In this embodiment, coating material  110  covers the entirety of the second pattern (corresponding to the land areas), as shown. However, more generally, coating material  110  covers at least a part of the second pattern, and does not substantially overlap the first pattern. Coating material  110  may therefore overlap some portion less than the entirety of the second pattern, or the entirety of the second pattern, as may be desired. 
       FIG. 4  shows a cross-sectional view of the embodiment of  FIG. 3 . Specifically, land areas  106  on golf ball  100  are selectively coated with coating material  110  to form golf ball  140 . As was discussed with respect to coating material  108 , coating material  110  should generally not be so thick as to significantly affect the aerodynamics of the golf ball, however coating material  110  may be applied in such a way as to achieve a desired dimple depth configuration. Accordingly, coating material  110  may have a thickness that is, for example, on the order of about 20 microns or less. In one embodiment, coating material  110  has a thickness of between about 1 micron and about 20 microns, inclusive and taking into account manufacturing tolerances. Coating material  110  may have a thickness that is slightly smaller than a thickness of coating material  108  for an equivalent moment of inertia of the golf ball, because coating material  110  is applied at a further radial distance from the center of the golf ball  140 . 
       FIGS. 5 and 6  show a further feature of the coating that may be used in conjunction with either of the above discussed embodiments. Specifically,  FIG. 5  shows several pockets  112  in the surface of cover layer  102 . Generally, pockets  112  are small indentations or abrasions intentionally formed in the surface of cover layer  102 . Pockets  112  generally have a depth  120  that is at least less than the depth of dimple  104 , and, in some embodiments, significantly less than the depth of dimples  104 . In embodiments where cover layer  102  has a thickness of about 2.0 mm, pockets  112  may have a depth  120  of less than about 0.5 mm, or less than about 0.3 mm, or less than about 0.1 mm. Furthermore, depth  120  may be an even shorter depth, such as less than about 20 microns, or generally of any value between about 1 micron and 20 microns, inclusive and taking into account manufacturing tolerances. 
     Pockets  112  may enable coating material  108  to better adhere to cover layer  102 . Pockets  112  may also allow more flexibility in the design of the golf ball, such as by achieving a desired moment of inertia without, for example, significantly changing the dimple depth or total diameter of the golf ball. 
     When coating material  110  is coated on cover layer  102  having pockets  112  therein, coating material  110  fills the pockets  112  as well as coats the surface of cover layer  102  with a top section  114  of coating material  110 . Top section  114  of coating material  110  may be left in place on the second pattern on top of land areas  106 , if desired, or may be removed to leave coating material  110  only in the pockets  112 .  FIG. 6  shows coating material  110  present only in pockets  112 . As shown in  FIG. 6 , coating material  110  is located in pockets  112 , but does not otherwise substantially overlap or extend over the top of the surface of cover layer  102 . 
       FIGS. 7 and 8  show an embodiment wherein dimple pockets  116 , which are similar to pockets  112  in that they are made or formed in the surface of cover layer  102 , but dimple pockets  116  are located in those portions of cover layer  102  which include dimple  104 . Similar to as discussed above with respect to  FIGS. 5 and 6 , coating material  108  may include a top section  118  as well as fill dimple pockets  116 . Top section  118  of coating material  108  may then be removed, if so desired, leaving coating material  108  only in pockets  116 . Dimple pockets  116  in or on or proximate to dimple  104  have a depth  122  that may be the same as or different from depth  120  of pockets  112  associated with land area  106 . 
     In these embodiments including pockets  112  and/or pockets  116 , generally, the coating material may be used to change the moment of inertia in accordance with this disclosure, without changing the diameter or aerodynamic performance of the golf ball. Therefore a wider range of golf ball designs may be used in accordance with the present disclosure, without the need to redesign the physical structure of the golf ball or sacrifice advantageous aerodynamic properties. 
     The golf ball in accordance with the present disclosure achieves an increased moment of inertia due to the density of the coating material being higher than the density of the core. As shown in  FIGS. 4-8 , generally, core  202  of the golf ball  100  has a first density, and coating material  108  or coating material  110  has a second density, where the second density is higher than the first density. The coating material  108  or  110  therefore increases the moment of inertia of the golf ball  130  or  140 , because more of the golf ball&#39;s mass is located at an outer radial distance from the golf ball&#39;s axis of rotation (the golf ball&#39;s axis of rotation being the golf ball&#39;s center of gravity). 
     The coating material may generally be any material having a density that is greater than the density of the core. A wide range of polymers are known in the art that may be manufactured to have high density values. Generally, the polymer making up the coating material may be any thermoplastic, thermoset, ionomer, copolymer, or other polymer material known and used in the art of golf balls so long as the polymer has a density that is greater than the density of the core. The density of a polymer coating material may be determined in accordance with ASTM D792, for example, or in accordance with other known measurement standards. 
     Additionally, the coating material may be a metal plating. Nearly any typical metal may be used, as most metals have a density that is significantly higher than the polymer materials conventionally used to form golf ball cores. Exemplary metals that may be used as the coating material include aluminum, steel, tungsten, titanium, magnesium, and iron alloys, and mixtures thereof, among a variety of other metals. The metal coating material may be selected based on density, hardness, workability, and cost effectiveness, for example, among other selection criteria. 
       FIG. 9  is a flowchart detailing a method of manufacturing the golf balls discussed above, including optional steps. Generally, a method  300  of manufacturing a golf ball includes first step  302  of receiving a golf ball having a core with a first density and a cover layer substantially surrounding the core, where the cover layer includes a plurality of dimples and at least one land area thereon. The plurality of dimples is arranged on the cover layer in a first pattern, and the at least one land area is arranged on the cover layer in a second pattern, the first and the second patterns being non-overlapping patterns. 
     The golf ball may then undergo an optional preliminary step of treating the cover layer so as to create pockets  112  in the cover layer. This preliminary treatment step may be, for example, a physical surface roughening, or a chemical etching that etches only a small portion of the cover layer such as an unmasked portion of the surface of the golf ball. 
     Next, method  300  of manufacturing the golf ball may take either of two general routes. In a first step  306  of a first route, the entire cover layer is coated with the coating material. The coating step  306  may be a physical coating step, such as by brushing, dipping, spraying or other physical application means. Alternatively, the coating step  306  may be a chemical coating step, such as chemical vapor deposition (CVD), plasma spray coating, or other chemical application means. The coating material is then selectively removed in step  308 , such that the coating material remains on only either of the first or second pattern, as desired. The removal of the coating material  308  may be a physical grinding away of the coating, or may be a chemical removal such as by chemical etching using a mask to protect selected coated areas to prevent the removal of selected coated areas. 
     Alternatively, in step  310  a mask may be applied over the golf ball. The mask may be a physical mask having a pattern of holes corresponding to either of the first pattern or the second pattern. The coating material is then  312  applied on top of the mask, after which  314  the mask is removed, leaving the coating material on only the pattern corresponding to the holes in the mask. 
     Finally, if the golf ball underwent step  304  to create pockets, the surface portion of the coating material  114  may be removed in step  316 . This step leaves the coating material in only the pockets, and not otherwise substantially overlapping the surface of the cover layer. Accordingly, a golf ball  130  or  140  is manufacturing having an increased moment of inertia as compared to a golf ball  100  prior to the manufacturing method  300 . 
     A comparative illustration of golf ball  100  with golf ball  140  is shown in  FIG. 10 . A golfer  400  swings a golf club  402  toward a golf ball on a tee. If the golf ball on the tee is golf ball  100 , then golf ball  100  will exhibit play characteristics as shown in the upper half of  FIG. 10  upon being struck by golf club  402 . Specifically, golf ball  100  will exhibit a high rate of rotation  508  around its center of gravity  512  because its moment of inertia, as graphically illustrated by the length  504  of moment arm  500 , is relative low. On the other hand, golf ball  140  exhibits a lower rate of rotation  510  about the center of gravity  512  because its moment of inertia, as graphically illustrated by the length  506  of moment arm  502 , is relatively high. Accordingly, golf ball  140  will display different play characteristics than golf ball  100 , and so may be more desirable to certain golfers based on the golfers&#39; preferences. 
     Furthermore, golf balls made in accordance with this disclosure may also simultaneously achieve improved play characteristics that are unrelated to the moment of inertia. Specifically, such golf balls may also achieve desired hardness patterns, as is fully described in U.S. Patent Application Publication No. 2011/0177884, entitled Golf Ball With Cover Having Varying Hardness, and filed on Jan. 20, 2010, the disclosure of which is hereby incorporated in its entirety. 
     While various embodiments of the invention have been described, the description is intended to be exemplary, rather than limiting and it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents. Also, various modifications and changes may be made within the scope of the attached claims.