Patent Grant
7326129
The present invention relates to a multi-piece golf ball comprising a plurality of layers, and a manufacturing method thereof.
Recently, several kinds of golf balls exhibiting both high bounce resilience and a soft feel when hit have been proposed. One example of such a golf ball is a multi-piece golf ball in which the ball is composed of a plurality of layers. Generally, in a multi-layered golf ball, especially in a golf ball that has three or more layers, a highly rigid core is covered with an interlayer that has relatively low rigidity, and the outer surface of the interlayer is covered with a hard cover. This arrangement aims to attain both high bounce resilience and a soft feel when hit by using the rigidity of the core and the softness of the interlayer. One example of such a multi-piece golf ball is disclosed in Japanese Examined Patent Publication No. 1991-52310.
However, such heretofore-known multi-layered golf balls aim to achieve both a long carry distance attained by the high bounce resilience property and a soft feeling when hit, which are inherently conflicting properties. Therefore, their performance in terms of carry distance may be unsatisfactory and there is room for further improvement.
One object of the present invention is to provide a multi-piece golf ball that can achieve a longer carry distance than heretofore-known golf balls, and a manufacturing method thereof.
The multi-piece golf ball of the present invention comprises a core, an interlayer, and a cover. The multi-piece golf ball aims to solve the above-descried problem. The core comprises a spherical main part and a plurality of ribs provided on the surface of the main part, the interlayer is inserted into depressions surrounded by the ribs, and the hardness of the interlayer is greater than that of the ribs.
In this arrangement, because the hardness of the interlayer is greater than that of the ribs, an excellent resilience property can be obtained, and even if the club head speed is slow, a satisfactory carry distance can be achieved. Furthermore, the following effects can be attained. When a golf club comes into contact with a golf ball, usually the ball is deformed in the circumferential direction due to friction generated between the ball and the clubface. When the deformed ball returns to its original condition due to elastic resistance, a force in the direction opposite to the direction of backspin is applied to the ball. At this moment, the greater the deformation of the deformed ball, the more the backspin is suppressed, and the longer carry distance can be achieved.
In the golf ball of the present invention, the ribs enhance the elastic resistance, which is the force applied when the ball is returning to its original condition, and therefore the backspin can be effectively reduced. More specifically, in this golf ball, because the hardness of the ribs is less than that of the interlayer, the ribs deform to a greater degree than the interlayer. The ribs are not mere protrusions but are structured so as to form walls surrounding the interlayer, and therefore when the ribs are returning to their original condition, the force of the entire wall strongly acts on the interlayer from the perimeter of the interlayer, and this increases the force opposing the backspin. As a result, a significantly longer carry distance can be achieved. This effect is particularly remarkable when the ball is hit by drivers, etc., which are designed to attain a long carry distance.
When an iron, in particular a short iron, is used, the striking direction is mainly in the direction tangential to the ball, and therefore a force in the circumferential direction acts on the ball. Therefore, the deformation of the interlayer in the circumferential direction is absorbed by the low-hardness ribs. As a result, when an iron is used, a soft feeling when hit can be obtained.
In the golf ball of the present invention, the core can be easily manufactured by molding the main part and ribs as a unit.
In the golf ball of the present invention, it is possible to make the hardness of the main part the same as the ribs. In this structure, because the hardness of the interlayer is greater than not only the ribs but also the main part, it is possible to reduce the amount of spin, and therefore attain an enhanced carry distance. Furthermore, when a ball is hit by an iron, since the force applied to the ball more effectively acts on the ribs and main part than on the interlayer, because they are softer than the interlayer, the soft feeling when hit can be enhanced.
In the golf ball of the present invention, it is also possible to make the hardness of the main part less than that of the ribs. In this structure, when a driver is used, because excess spin can be easily suppressed, it is possible to increase the launch angle and obtain a longer carry distance.
In the golf ball of the present invention, it is further possible to make the hardness of the main part greater than that of the interlayer. In this structure, the bounce resilience of the ball is enhanced by increasing the hardness of the main part, and accordingly the carry distance can be increased.
In the golf ball of the present invention, it is yet further possible to make the hardness of the main part greater than that of the ribs but less than that of the interlayer. In this structure, by suitably selecting the spin amount and resilience property in accordance with the head speed, etc., it is possible to increase the carry distance.
In the above-described structure of a golf ball, the height of each rib as measured from the surface of the main part is preferably 2.0 to 11.0 mm, and more preferably 5.0 to 10.5 mm. When the rib height is greater than 2.0 mm, the thickness of the interlayer of high hardness is prevented from becoming too thin, and a satisfactory resilience property can be maintained. When the rib height is less than 11.0 mm, the thickness of the interlayer is prevented from becoming too thick, which would otherwise cause a hard feeling when hit.
In the above-described golf ball, various rib structure configurations are possible. In order to obtain a long carry distance by having tall ribs, the height of each rib, measured from the surface of the main part, is preferably 6.4 to 11.0 mm, and more preferably 8.0 to 10.5 mm. In this case, it is preferable that each rib extend in such a manner that its width increases from the cover to the core, and that depressions be formed into cone-like shapes by the side faces of the ribs. In this structure, because the width of each rib is greater at the base than the top, it is possible to prevent the rib from collapsing when pressure is applied during molding. In particular, this structure is advantageous in the present invention because the hardness of the ribs is low.
In this structure, the proportion held by the interlayer gradually decreases towards the center of the ball, and accordingly the proportion held by the low-hardness ribs increases. Therefore, the influence of impact is lessened towards the center of the ball; however, because the proportion held by the low-hardness ribs increases, deformation of the ribs can be ensured. As a result, the taller the ribs become, the greater the force reducing the backspin should be, further increasing the carry distance.
In the present invention, “cone-like shape” refers to a shape such that each depression forms a somewhat conical region by being surrounded by rib side faces, and the area of a plane formed by cutting the region along a spherical surface having the same central point as the core decreases as the cutting surface moves from the cover to the core. The shape of the above-described plane is not limited and may be, e.g., polygonal as well as circular. In some embodiments, the depression is formed into a cone-like shape by being surrounded only by ribs, while in other embodiments, the main body is exposed at the bottom of the depression, and the side faces of the ribs and the main body together define the cone-like shape. However, even when the main body is exposed, the exposed area thereof is small and a cone-like shape is formed as a whole.
When the height of the ribs is increased, the diameter of the main part becomes smaller. This makes it easier to mold the core. In other words, in prior-art golf balls, if the diameter of the core is large, when the core is formed from, for example, a rubber composition, it is difficult to satisfactorily vulcanize the center thereof, and this varies the hardness of the core along the radial direction. In contrast, if the diameter of the main part of the core is relatively small as described above, it is possible to satisfactorily vulcanize the center of the core, and therefore a core having a uniform hardness can be obtained.
In the above-described golf ball, it is also possible to arrange the ribs such that each of the ribs comprises at least one notch so as to form a passageway between adjacent depressions. Forming notches in the ribs has the following advantages during manufacturing. For example, when a golf ball of the present invention is manufactured by molding a core, placing it in a mold together with a material for the interlayer, and press molding, because the adjacent depressions communicate with each other via the notches, when press molding is conducted, the material for the interlayer spreads throughout the depressions through the notches. This makes it unnecessary to separately insert the material for the interlayer into each of the depressions, simplifying the manufacturing equipment and reducing the manufacturing time. When the interlayer is formed by injection molding, the interlayer can be formed by using one or a small number of gates, thus reducing the production equipment cost.
It is preferable that the ribs extend along three great circles on the surface of the main part, intersecting each other at right angles, that each arc section partitioned by the intersections of the great circles is provided with at least one notch, that each notch has a plane extending along the arc section from one point on a normal line on the core that passes through the intersection of the great circle, and that the plane has an angle not smaller than 90° relative to the normal line. Four depressions that are arranged so as to have their common center at an intersection of the great circles are thus made to communicate with each other, and the material for the interlayer can readily spread between them. Because the angle made between the plane and the normal line is not smaller than 90°, the angle serves as a draft angle, and, for example, when the core is molded using two molds, such as an upper mold and a lower mold, the core can be easily removed from the mold.
From the viewpoint of making adjacent depressions communicate with each other, it is possible to form a notch in the middle of the arc section in the arc direction. It is preferable that such a notch have two planes that both extend toward the intersection from a point on the normal line of the spherical body that passes through the mid point of each arc section in the arc direction, wherein the angle made between the planes and the normal line is 45 to 48°. This arrangement allows the above angle made between the planes and the normal line to serve as a draft angle, so that the core can be removed from the mold easily.
In the present invention, by shaping the ribs as described above, even when the core is molded using two molds, the core can be easily removed from the mold. In other words, if a protrusion is simply formed, the protrusion may snag, thus preventing the core from being removed from the mold and making manufacturing impossible. However, by arranging the ribs as described above, even if a protrusion is formed on the main part, the core can be easily removed from the mold. As a result, productivity can be improved.
To solve the above-described problem, a method for manufacturing a multi-piece golf ball of the present invention having a core, an interlayer, and a cover comprises the steps of preparing a first mold that comprises a base having a spherical surface, and a cavity having a plurality of grooves formed along the surface of the base, the grooves being substantially the same depth as each other as measured from the surface; molding a core having a plurality of ribs on the surface of a spherical main part by inserting a core material into the cavity of the first mold; preparing a second mold having a spherical cavity corresponding to the outermost diameter of the core; molding an interlayer whose hardness is greater than that of the core by placing the core taken from the first mold in the cavity of the second mold, and inserting an interlayer material into depressions surrounded by the ribs; and molding a cover over the second interlayer.
By employing this manufacturing method, it is possible to obtain a multi-piece golf ball that can achieve a greatly increased carry distance as described above. In the second mold, because the cavity corresponds to the outermost diameter of the core, it is possible to insert an interlayer material with the ribs in contact with the surface of the cavity. Therefore, the core can be easily centered, and this makes it possible to accurately align the center of each layer.
The above-described manufacturing method explains one embodiment wherein the main part and the ribs are molded as a unit. This arrangement allows the hardness of the main part to be substantially the same as that of the ribs. In contrast, a golf ball in which the hardness of the main part differs from that of the ribs can be manufactured by the following method. In other words, one of the other methods for manufacturing a multi-piece golf ball of the present invention having a core, an interlayer, and a cover that solves the above-described problem comprises the steps of molding a spherical main part; preparing a first mold comprising a cavity having a spherical receiving part that corresponds to the surface of the main part and a plurality of grooves formed along the surface of the receiving part, the grooves being substantially the same depth as measured from the surface; molding the core having a plurality of ribs on the surface of the main part by placing the main part in the receiving part of the first mold and inserting a material having a hardness different from that of the main part into the cavity; preparing a second mold having a spherical cavity corresponding to the outermost diameter of the first interlayer; molding an interlayer whose hardness is greater than that of the core by placing the core taken from the first mold in the cavity of the second mold, and inserting a material having a hardness different form that of the ribs into a depressions surrounded by the ribs; and molding a cover over the interlayer.
In the above-described manufacturing method, a core comprising a spherical main part and ribs provided on the surface of the main part are molded. In the first mold, if the depth of each groove measured from the base is 6.4 to 11.0 mm, it is possible to manufacture a golf ball having a suitable bounce resilience property because the hard interlayer is relatively thick. When the core comprises a rubber composition, and the diameter of the main part is relatively small, it is possible to satisfactorily vulcanize the core, including around the center thereof, and to mold a core with little variation in hardness without decreasing its hardness near the center.
By arranging the cavity of the first mold so that a plurality of grooves communicate with one other to form at least one enclosed region, and so that at least one shallower portion is formed in the grooves, notches as described above can be formed in the ribs. This allows the material for the interlayer to spread throughout the depressions in the interlayer molding step.
Hereunder, a multi-piece golf ball of a first embodiment of the present invention is explained with reference to drawings.
As shown in
The core 3 is composed of a rubber composition, and, as shown in
It is preferable that the diameter of the main part 9 be 15.4 to 37.3 mm, and that the height of the rib 11 be 2.0 to 11.0 mm. To obtain a soft feeling when hit, the Shore D hardness of the core 3 is preferably 38 to 58, and more preferably 42 to 48.
As shown in
The interlayer 5 is composed of a rubber composition or an elastomer, covers the surface of the core 3, and its outline forms a substantially spherical shape. As shown in
The cover 7 is composed of an elastomer, and covers the top portions of the ribs 11 and the interlayer 5, with predetermined dimples (not shown) being formed on the outer surface of the cover 7. It is preferable that the thickness of the cover 7 be 0.8 to 2.6 mm, and more preferably 1.6 to 2.0 mm. The thickness of the cover 7 may be set outside this range; however, if the thickness of the cover 7 is less than 0.8 mm, the durability of the cover decreases remarkably and molding becomes difficult. On the other hand, if it exceeds 2.6 mm, the impact feel becomes too hard. It is preferable that its Shore D hardness be 56 to 68. Note that the thickness of the cover 7 is defined as the distance from an arbitrary point on the outermost part in the outward radial direction where no dimple is formed to an arbitrary point that comes into contact with the interlayer that is measured along the normal line.
The materials constituting the components of the above-described golf ball are explained in detail. The core 3 can be manufactured using a known rubber composition comprising a base rubber, a cross-linking agent, an unsaturated carboxylic acid metal salt, a filler, etc. Specific examples of the base rubber include natural rubber, polyisobutylene rubber, styrenebutadiene rubber, EPDM, etc. Among these, it is preferable to use high-cis polybutadiene that contains 40% or more, and preferably 80% or more cis-1,4-bonds.
Specific examples of cross-linking agents include dicumyl peroxide, t-butylperoxide, and like organic peroxides; however, it is particularly preferable to use dicumyl peroxide. The compounding ratio of the cross-linking agent is generally 0.3 to 5 parts by weight, and preferably 0.5 to 2 parts by weight per 100 parts by weight of the base rubber.
As metal salts of unsaturated carboxylic acids, it is preferable to use monovalent or bivalent metal salts of acrylic acid, methacrylic acid, and like C3 to C8 unsaturated carboxylic acids. Among these, the use of zinc acrylate can improve the ball bounce resilience and is particularly preferable. The compounding ratio of the unsaturated carboxylic acid metal salt is preferably 10 to 40 parts by weight per 100 parts by weight of base rubber. This is because, a compounding ratio of less than 10 parts by weight will decrease the ball bounce resilience and shorten the carry distance. If the compounding ratio exceeds 40 parts by weight, the ball becomes too hard and the soft feeling is deteriorated.
Examples of the filler include those generally added to cores. Specific examples thereof include zinc oxide, barium sulfate, calcium carbonate, etc. The preferable compounding ratio of the filler is 2 to 50 parts by weight per 100 parts by weight of base rubber. If necessary, it is also possible to add an antioxidant, a peptizer, and the like.
The interlayer 5 is composed of a rubber composition or elastomer as described above. When a rubber composition is used, the same materials as used for the core 3 described above can be used. However, it is preferable that the compounding ratio of unsaturated carboxylic acids be increased to make the interlayer harder than the core 3.
When the interlayer 5 is composed of an elastomer, it is possible to use, for example, a styrene/butadiene/styrene block copolymer (SBS), a styrene/isoprene/styrene block copolymer (SIS), a styrene/ethylene/butylene/styrene block copolymer (SEBS), a styrene/ethylene/propylene/styrene block copolymer (SEPS), or like styrene-based thermoplastic elastomer; an olefin-based thermoplastic elastomer having polyethylene or polypropylene as a hard segment and butadiene rubber, acrylonitrile butadiene rubber or ethylene/propylene rubber as a soft segment; a vinyl chloride-based plastic elastomer having crystallized poly(vinyl chloride) as a hard segment and amorphous poly(vinyl chloride) or an acrylonitrile butadiene rubber as a soft segment; a urethane-based plastic elastomer having polyurethane as a hard segment and polyether or polyester urethane as a soft segment; a polyester based plastic elastomer having polyester as a hard segment and polyether or polyester as a soft segment; an amide based plastic elastomer having polyamide as a hard segment and polyether or polyester as a soft segment; an ionomer resin, etc.
It is possible to form the cover 7 using an elastomer having almost the same components as those used for the interlayer.
As described above, in the present embodiment, because the interlayer 5 is injected into a depressions 13 surrounded by the ribs 11, in the place where the interlayer 5 contacts the inner surface of the cover 7, the proportion of the interlayer 5 is greater than that of the ribs 11. Therefore, when a ball is hit, most of the striking force acts on the harder interlayer 5. This makes it possible to obtain high bounce resilience property even with a low head speed, and increase the carry distance. Having the above-described structure also has the following advantage. When a golf club hits a golf ball, the ball is usually twisted in the circumferential direction dues to the friction between the ball and the clubface. When the twisted ball returns to its original condition due to elastic resistance, a force opposite to the backspin is applied to the ball. At this moment, the greater the deformation of the twisted ball is, the more the backspin is suppressed, and the longer the carry distance is.
In the golf ball of the present embodiment, the backspin can be effectively reduced because the ribs 11 enhance the elastic resistance, which is a force applied when a ball is returning to its original condition. More specifically, as shown in
The above-described ribs may be formed into various shapes; however, from the viewpoint of effectively molding the interlayer, it is preferable to provide a notch in the rib having a structure as described below. As shown in
When the notch 24 is formed as described above, it is preferable that the length of the notchless top portion of each arc section S of the ribs in the arc direction, divided at the intersection P, as shown in
As shown in
It is also possible to provide a notch in the middle of the arc section S of the rib 11 in the arc direction. As shown in
Alternatively, as shown in
As shown in
In the above-described embodiment, the thickness of the interlayer 5 and the height of the rib 11 are the same; however, they do not necessarily have to be the same. For example, it is possible to make the thickness of the interlayer 5 greater than the height of the rib 11. However, it is preferable that the thickness of the interlayer 5 be slightly greater than the height of the rib 11, for example, by 1.5 mm or less.
One example of a method for manufacturing a golf ball having the above-described structure is explained next with reference to drawings. This manufacturing method, wherein an interlayer is formed from a rubber composition, is explained below.
First, as shown in
Then, as shown in
As shown in
At this time, the rubber compositions 61 placed on the core 3 and in the depression 41 of the lower mold 45 fill the depressions 13 while being pressed against the surface of the core 3. As described above, the two adjacent depressions 13 communicate with each other through notches 24, and therefore the rubber composition spreads throughout each depression and uniformly fills the space therein. The interlayer 5 may also be molded by injection molding using, for example, a mold as shown in
When the molding of the interlayer 5 is completed, the core 3 covered with the interlayer 5 is removed from the mold. Thereafter, a cover 7 is applied to the surface of the interlayer 5 by press molding or injection molding in such a manner that the cover has predetermined dimples, thus obtaining a three-piece golf ball.
As described above, notches 24 are provided in the ribs 11 and the two adjacent depressions 13 communicate with each other through the notches 24, and therefore the rubber composition 61 spreads throughout the depressions and uniformly fills the space therein when pressed from any position on the surface of the core 3. It is thus possible to cover the core 3 with the interlayer in a single press molding step. As a result, the manufacturing time can be significantly reduced.
A method for manufacturing a golf ball comprising an interlayer with notches is explained above. However, a golf ball without notches can also be manufactured by almost the same method. However, when notches are not provided, it is necessary to conduct press molding by arranging the interlayer material so as to spread throughout the depressions, or, when injection molding is conducted, a plurality of gates corresponding to the depressions must be provided.
In the golf ball of the present invention, because the interlayer is harder than the core and has an effect on the bounce resilience property, it is possible to vary the characteristics of the ball by changing the thickness of the interlayer. For example, the thicker the interlayer becomes, the more the golf ball will be suited for a club such as a driver, which is designed for obtaining a longer carry distance. In other words, when a driver is used, the striking direction is mainly directed toward the center of the ball, and therefore the thicker the interlayer becomes, the more it is possible to prevent the striking force from being transferred to the low-hardness core. This reduces the deformation amount of the ball and increases its resilience. As a result, it is possible to increase the carry distance. However, because the interlayer is harder than the core, if the height of the ribs is increased, the thickness of the high-hardness interlayer is accordingly increased. This results in a hard feeling when the ball is hit.
Rather than merely increasing the height of the ribs and the thickness of the interlayer as described above, the rib and interlayer structure described below makes it possible to further increase the carry distance. This is described in detail in the second embodiment.
A second embodiment of the multi-piece golf ball of the present invention is explained next with reference to the drawings.
Each of the ribs 132 extends along one of three great circles drawn around the main part 131 so as to intersect each other at right angles. Eight depressions 133 are formed in the surface of the main part 131 by the ribs 132. The height of the ribs 51 is preferably 5.0 to 11.0 mm, and more preferably 7.0 to 9.0 mm. The height of the ribs 132 may be outside the above range; however, collapsing of the ribs can be prevented during the manufacturing process by setting the height of the ribs not to exceed 11.0 mm.
As shown in
The interlayer 5 has a thickness that is almost the same as the height of the ribs 132 and is inserted into the eight depressions 133 surrounded by the ribs 132, with its outline forming a substantially spherical shape. As shown in
The cover 7 covers the top portions of the ribs 132 and the interlayer 5, with predetermined dimples (not shown) being formed on the outer surface of the cover 7. The thickness of the cover 7 is preferably 0.8 to 2.6 mm, and more preferably 1.6 to 2.0 mm. As with the first embodiment, the Shore D hardness of the cover 7 is preferably 56 to 68.
The materials of the core 3, interlayer 5, and cover 7 may be the same as those used in the first embodiment.
In the thus-formed golf ball 1, even if the ribs 132 are comparatively tall, because the width of the base portion of the ribs 132 is greater than the top portion thereof, it is possible to prevent the ribs 132 from collapsing when pressure is applied during molding. Because the ribs of the golf ball are relatively soft, having the above-explained structure is particularly advantageous. Furthermore, because the thickness of the high-hardness interlayer 5 becomes greater in relation to this rib 132 height, it is possible to obtain a high bounce resilience property. Therefore, even at a slow head speed, a long carry distance can be achieved.
As shown in
Also, because the ribs 132 become longer, the diameter of the main part 131 of the core 3 becomes smaller, and therefore it is possible to satisfactorily vulcanize the core 3 including around the center thereof, obtaining a core 3 without variations in hardness. This reduces the manufacturing time as well.
It is also possible to form notches in the ribs of the golf ball of the present embodiment in the same manner as in the first embodiment. As shown in
By forming notches 321 in this manner, four depressions 133 that are disposed so as to have their common center at an intersection P of the great circles are made to communicate with each other, and the material for the interlayer can readily spread between the depressions 133 via the notches 321. In this case, as shown in
It is also possible to form a notch in the middle of the arc section S formed between each intersection P of each rib 132. In other words, as shown in
Note that the golf ball of the present embodiment has almost the same arrangement as that of the first embodiment except for the height and shape of the rib, and therefore the same method explained in the first embodiment (
A third embodiment of the multi-piece golf ball of the present invention is explained below with reference to drawings.
The main part 231 can be manufactured using a known rubber composition comprising a base rubber, a cross-linking agent, an unsaturated carboxylic acid metal salt, filler, etc. Specific examples of the base rubber include natural rubber, polyisobutylene rubber, styrenebutadiene rubber, EPDM, etc. Among these, it is preferable to use high-cis polybutadiene that contains 40% or more, and preferably 80% or more cis-1,4-bonds.
Specific examples of cross-linking agents include dicumyl peroxide, t-butylperoxide, and like organic peroxides; however, it is particularly preferable to use dicumyl peroxide. The compounding ratio of the cross-linking agent is generally 0.3 to 5 parts by weight, and preferably 0.5 to 2 parts by weight per 100 parts by weight of the base rubber.
As for metal salts of unsaturated carboxylic acids, it is preferable to use monovalent or bivalent metal salts of acrylic acid, methacrylic acid, and like C3 to C8 unsaturated carboxylic acids. Among these, the use of zinc acrylate can improve the ball's bounce resilience and is particularly preferable. The compounding ratio of the unsaturated carboxylic acid metal salt is preferably 10 to 40 parts by weight per 100 parts by weight of base rubber.
Examples of filler include those generally added to cores. Specific examples thereof include zinc oxide, barium sulfate, calcium carbonate, etc. The preferable compounding ratio of the filler is 2 to 50 parts by weight per 100 parts by weight of base rubber. If necessary, it is also possible to add an antioxidant, a peptizer, and the like.
Note that not only the above-mentioned rubber compositions but also known elastomers can be used as the material for the main part 231.
As shown in
The ribs 232 are composed of a rubber composition, and the same materials for the main part 231 described above can be used. However, in the present embodiment, by changing the compounding ratio of the unsaturated carboxylic acid or organic peroxide of the ribs 232 from that of the main part 231, the hardness of the main part 231 is differentiated from that of the ribs 232. For example, by increasing the amounts of the unsaturated carboxylic acid and organic peroxide in the rib 232, it is possible to make the hardness of the ribs 232 greater than that of the main part 231.
As shown in
The interlayer 5 may be composed of a rubber composition or an elastomer having almost the same components as that of the ribs 232. When the interlayer 5 is composed of a rubber composition, it is preferable that the compounding ratio of the unsaturated carboxylic acid and organic peroxide be increased to make its hardness greater than that of the ribs 232. When the interlayer 5 is composed of an elastomer, the elestomer can be one of those used for the interlayer 5 in the first embodiment.
As shown in
In the golf ball of the present embodiment, it is also possible to form notches in the ribs 232 in the same manner as in the second embodiment (see
In the golf ball of the present embodiment, because the hardness of the interlayer 5 is greater than that of the ribs 232, as with the first and second embodiments, it is possible to increase the carry distance while maintaining a soft feeling when the ball is hit with an iron.
Furthermore, by varying the hardness of the main part 231 in responses to needs, desired properties can be obtained. In other words, by making the hardness of the main part 231 lower than that of the ribs 232, when a driver is used, excess spin can be easily suppressed, and therefore it is possible to increase the launch angle and obtain a longer carry distance. At the same time, by making the hardness of the main part 231 greater than that of the interlayer 5, the bounce resilience of the ball is enhanced and the carry distance is increased.
By setting the hardness of the main part 231 in the above-described range, i.e., greater than the hardness of the rib 232 and the less than that of the interlayer 5, it is possible to suitably select the spin amount and resilience property depending on the head speed, etc., to increase the carry distance.
The golf ball of the present embodiment can be manufactured, for example, by the method described below.
First, a main part 231 is formed by press molding a rubber composition in a mold, for example, at 130 to 160° C. for 5 to 25 minutes. Here, the main part 231 may be composed of an elastomer as described above. In this case, the main part 231 can be formed by press molding or injection molding. Next, the thus-formed main part 231 is placed in a first mold 102 as shown in
As shown in
Subsequently, the core 3 comprising the main part 231 and the ribs 232 is removed from the first mold 102, and placed in the second mold 104. As shown in
As shown in
Here, the rubber composition N placed on the core 3 and in the cavity 141 of the lower mold 104a fill the depressions 233 while being pressed against the surface of the semifinished product. As described above, the adjacent depressions 233 communicate with each other through notches 321, and therefore the rubber composition spreads throughout the depressions 233 and uniformly fills the space therein. As described above, the interlayer 5 may be formed by injection molding (see
As described above, a notch is provided in each rib 232 and the adjacent depressions 233 communicate with each other through the notch, and therefore the rubber composition N spreads throughout the depressions 233 and uniformly fills the space therein when pressed from any position on the surface of the core 3. Therefore, it is possible to easily cover the core 3 with the interlayer 5, significantly reducing the manufacturing time. Here, the interlayer 5 is composed of a rubber composition, but it is also possible to form the interlayer 5 with an elastomer. When an elastomer is used, the interlayer 5 may be formed by injection molding.
When the molding of the interlayer 5 is completed, a semifinished product comprising a main part 231, ribs 232 and an interlayer 5 is removed from the second mold 104. Subsequently, by covering the semifinished product with the cover 7 by press molding or injection molding in such a manner that the cover 7 has predetermined dimples thereon, a golf ball of the present embodiment is obtained.
Note that, a golf ball comprising an interlayer 5 with notches is explained above; however, it is also possible to form a golf ball comprising an interlayer 5 without notches in almost the same manner. When notches are not provided, it is necessary to conduct press molding by positioning the interlayer material so that the material can be inserted into each of the depressions, or, when injection molding is conducted, a plurality of gates corresponding to each depression must be provided.
One example of a method for manufacturing the golf ball of the present embodiment is explained above. In the manufacturing method of the present invention, by suitably selecting the materials for the main part 231, ribs 232, and interlayer 5, it is possible to control the hardness of each component, and this makes it possible to easily manufacture a golf ball having the desired properties as described above.
Examples of the present invention and Comparative Examples will be explained below. First, nine types of golf balls according to the present invention are compared with three types of golf balls according to Comparative Examples. The Examples correspond to the first and second embodiments of the present invention.
Table 1 shows the compounding ratio (parts by weight) of the materials for the golf balls of Examples 1-9 and Comparative Examples 1-3. Table 2 shows the thickness of the interlayer (height of the ribs), whether ribs are provided or not, and the hardness (Shore D hardness) of each component of the golf balls.
The golf balls of Examples 1 and 5 comprise a core having the same structure as that of the core 3 in the first embodiment as shown in
The golf balls of Examples 3, 4 and 6 comprise a core having the same structure as that of the core 3 in the second embodiment as shown in
The golf balls of Examples 2, 7, 8 and 9 correspond to the second embodiment, wherein the core has the same structure as that of the core 3 as shown in
Comparative Examples 1-3 are conventional three-piece golf balls wherein no ribs are provided on the core, and the core, the interlayer and the cover are formed concentrically. Comparative Examples 1 to 3 respectively correspond to Examples 1, 2 and 4 with respect to the thickness of the interlayer and the hardness of each component.
Using the golf balls obtained in the Examples and Comparative Examples, which have the above-described structures, hitting tests were conducted using a hitting robot (manufactured by Miyamae Co., Ltd.: product name “SHOT ROBO V”) with a number one wood (1W: Mizuno Corporation; Mizuno 300S-II 380, loft angle: 9°, length: 44.75 inches (113.66 cm), shaft flex: S) and a number five middle iron (5I: manufactured by Mizuno Corporation; T-ZOID•MX-15, loft angle: 27°, length: 37.5 inches (95.25 cm), shaft flex: S), and the carry distances were measured. The head speed of the 1W was set at 45 m/s and that of the 5I was set at 35 m/s. Tests of the feeling when the balls were hit (impact feeling) were conducted by ten amateurs using a 1W and a 5I. The ten amateurs were asked to select either 1: soft, 2: slightly soft, 3: fair, 4: slightly hard, or 5: hard to evaluate the feeling when the balls were hit and the average value of all values selected was defined as the feeling value for each Example and Comparative Example. Tables 24 and 25 show graphs of the results.
The golf balls of Examples 1, 2 and 4 are compared with those of Comparative Examples 1 to 3 having the same interlayer thickness and the same hardness in each component. As is clear from Table 3, the golf balls of Examples 1, 2 and 4 attained a softer feeling when hit using an iron, and a longer carry distance using a driver. It is assumed that this is because the bounce resilience property of the balls is enhanced due to the interlayer disposed in a depression surrounded by ribs, due to the fact that, as shown in
The feeling when the ball was hit using an iron for Examples 1, 2 and 4 are compared with that of Comparative Examples 1 to 3. As shown in
From the comparison between Example 5 and Examples 1 to 4, it is clear that when the ribs become shorter than a certain height, the bounce resilience property of the ball is decreased and there is a tendency for the carry distance to exhibit difficulty in increasing because the thickness of the high-hardness interlayer also decreases. In contrast, a comparison of Example 6 and Examples 1 to 4 shows that when the ribs are tall to some degree, the interlayer becomes thicker and this results in a hard feeling when the ball is hit.
In Example 7, the difference in hardness between the core and the interlayer is 11. When the hardness of the interlayer exceeds the hardness of the core to a certain degree, the hardness of the interlayer becomes noticeable and therefore the ball tends to feel hard when hit. In particular, when the ball is hit with an iron whose head speed is relatively slow, it is evaluated as feeling very hard.
In contrast, in Example 8, the difference in hardness between the core and the interlayer is 1. When the difference in hardness is so small, the deformation of the ribs is small and the force opposing the backspin of the ball becomes less. This makes it difficult to obtain a long carry distance.
In Example 9, both the core hardness and the interlayer hardness are high, and therefore the ball feels hard when hit and the longest carry distance was obtained in all Examples and Comparative Examples.
Hereunder, Examples corresponding to the third embodiment of the present invention and Comparative Examples are explained.
Table 4 shows the hardness (Shore D hardness) of the components composing the golf balls of Examples 10 to 12 and Comparative Example 4. In Examples 10 to 12 and Comparative Example 4, the thickness of the main part composing the core is 23.3 mm, and the thickness of the interlayer is 8 mm. Table 5 shows the compounding ratio of materials for obtaining the hardnesses shown in Table 4. The cover 7 that was used was the same as that of Example 1 (Shore D hardness 62), and other examples.
Example 10 is a golf ball wherein the hardness of the main part 231 of the third embodiment as shown in
Using the golf balls obtained in the Examples and Comparative Examples described above, hitting tests were conducted using a hitting robot (manufactured by Miyamae Co., Ltd.: product name “SHOT ROBO V”) with a No. 1 Wood (1W: Mizuno Corporation; Mizuno MP-001, loft angle: 9.5°, shaft: Tour Sprit MP carbon shaft (length: 45 inches (114.3 cm), shaft flex: S), and the carry distances were measured. The head speed of the 1W was set at 43.5 m/s, and the ball of each Example and Comparative Example was hit five times. The average carry distance of the five hits was defined as the carry distance for each Example and Comparative Example. Tests of the feeling when the ball was hit were also conducted by ten amateurs using a 1W in the same manner as described above. Table 6 shows the results.
As is clear from Table 6, compared to the golf ball of Comparative Example 4, the backspin is reduced and the launch angle is increased in each of the golf balls of Examples 10 to 12, obtaining a longer carry distance than that of Comparative Example 4.
As described above, a multi-piece golf ball of the present invention can significantly increase the carry distance.
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