Golf ball

Details Golf ball Golf ball

1999-06-18

2001-07-31

Shoap, Allan N. (Department: 3729)

Games using tangible projectile

Golf

Ball

C473S367000, C473S368000, C473S371000, C473S374000, C473S377000, C473S378000, C473S600000, C473S601000, C473S602000

Reexamination Certificate

active

06267695

ABSTRACT:

This invention relates to a golf ball comprising a core, a cover inner layer, and a cover outer layer, and more particularly, to such a golf ball in which the cover outer layer penetrates into the cover inner layer to form protrusions therein.
BACKGROUND OF THE INVENTION
A variety of studies and proposals have been made to find a good compromise between flight distance and “feel” of golf balls. For solid golf balls comprising a solid core and a cover, one common approach is to construct the core and the cover into multilayer structures for adjusting their hardness and dimensions (including diameter and gage).
For example, U.S. Pat. No. 5,439,227 discloses a three-piece golf ball comprising a core, a cover inner layer and a cover outer layer, the cover outer layer being harder than the cover inner layer. U.S. Pat. No. 5,490,674 discloses a three-piece golf ball comprising a solid core of inner and outer layers and a cover, the core inner layer being harder than the core outer layer.
While the respective layers of most golf balls define smooth spherical surfaces, the golf balls disclosed in U.S. Pat. Nos. 2,376,085 and 5,692,973 have a core which is provided with outwardly extending protrusions for preventing the core from being offset during injection molding of the cover therearound. The protrusions in these golf balls are substitutes for the support pins used during injection molding. These patents do not attempt to positively utilize the shape effect of support pin-substituting protrusions, but rather intend to avoid incorporation of a distinct material in the cover, by forming the protrusions from the same material as the cover.
Recently, JP-A 9-285565 proposes a two-piece solid golf ball in which the solid core and cover, or adjoining layers of a multilayer solid core or adjoining layers of a multilayer cover are provided with irregularities. When hit, the ball gives a different feel to the player, depending on the loft angle of the particular club with which it is struck. This golf ball is improved in feel, but insufficient in flight performance and spin. There is however, room for further improvement.
SUMMARY OF THE INVENTION
An object of the invention is to provide a golf ball comprising a core, a cover inner layer and a cover outer layer wherein the cover inner layer is formed with recesses and the cover outer layer is formed with protrusions fitted in the recesses, thereby achieving a soft feel, a low spin rate when hit with a small loft angle club, good flight performance, and good control when hit with an iron or sand wedge.
It is well known from the study of strength of materials that a beam or column supporting an axial compressive load gives rise to the buckling phenomenon that as the load increases, uniform compression becomes unstable and is shifted laterally whereby the beam is bent. The invention has been made by applying the buckling phenomenon to a golf ball. Specifically, when columns or protrusions of different hardness are distributed in a surface-adjoining region of a ball undergoing a large amount of deformation, specifically the cover inner layer, the behavior of vertical and horizontal components of the deformation that the ball undergoes upon impact is made different from conventional balls. Then the dependency on club of initial conditions (especially spin rate) of the ball can be adjusted as desired.
The invention provides a golf ball comprising a core and a cover enclosing the core, wherein the cover consists essentially of an outer layer and an inner layer having a lower hardness than the outer layer, the cover inner layer is formed with a plurality of recesses in its outer surface and the cover outer layer is formed over the cover inner layer in such a manner that the cover outer layer penetrates into the recesses in the cover inner layer to form convex protrusions. It has been found that the sum of the cross-sectional areas of the protrusions at their base and the height of the protrusions in a normal direction should be in specific ranges; or the protrusions of the cover outer layer fitted in the recesses in the cover inner layer should satisfy a specific relationship to the thickness of the cover outer layer. The construction where the protrusions on the cover outer layer are fitted in the recesses in the cover inner layer in an optimum manner has the following advantages. For driver shots, due to the relationship between a high head speed and a small loft angle, the impact force has a greater vertical component relative to the club face so that the protrusions embedded within the cover inner layer give rise to a buckling phenomenon (the ball is liable to collapse), which provides a reduced spin rate and an increased launch angle, resulting in a drastically increased carry. For short iron shots, due to the loft angle, the impact force has a greater horizontal component relative to the club face. Since the protrusions within the cover inner layer do not give rise to a buckling phenomenon except for the vertical component, satisfactory spin performance is obtained.
In a first aspect, the invention provides a golf ball comprising a core and a cover enclosing the core, wherein the cover consists essentially of an outer layer and an inner layer having a lower hardness than the outer layer, the cover inner layer is formed with a plurality of recesses in its outer surface and the cover outer layer is formed over the cover inner layer in such a manner that the cover outer layer penetrates into the recesses in the cover inner layer to form protrusions, the sum of the cross-sectional areas of the protrusions at their base accounts for 2 to 45% of the surface area of the cover inner layer provided that the cover inner layer is not formed with the recesses, and the protrusions have a height in a normal direction of at least 30% of the thickness of the cover inner layer where no recesses are formed.
In a second aspect, the invention provides a golf ball comprising a core, a cover inner layer and a cover outer layer, wherein the cover outer layer has a higher hardness than the cover inner layer, the cover inner layer is formed with a plurality of recesses in its outer surface and the cover outer layer is formed over the cover inner layer in such a manner that the cover outer layer penetrates into the recesses in the cover inner layer to form protrusions, the protrusions of the cover outer layer fitted in the recesses in the cover inner layer satisfy the following relationship:
0.2
⁢
T
⁣
<
2
⁢
A
N
×
1
π
<
5
⁢
T
wherein A is the sum (mm
2
) of the cross-sectional areas of the protrusions at their base, N is the number of protrusions, and T is the thickness (mm) of the cover outer layer where no protrusions are formed.
When the ball is struck at a relatively high club head speed as with a driver so that the ball is given a large impact force, that force acts to cause the protrusions to buckle. On the other hand, when the ball is struck at a relatively low head speed as with a short iron so that the ball is given a small impact force, the protrusions do not buckle. In the former case of large impact force, the protrusions buckle so that the strength of the protrusions of the cover outer layer embedded in the cover inner layer does not substantially act and only the strength of the cover inner layer formed softer than the protrusions contributes. This results in a reduced spin rate and an increased carry. In the latter case of small impact force, the protrusions do not buckle so that the strength of the cover inner layer in a substantial sense is a combination of the strength of the cover inner layer in itself and the strength of the protrusions embedded therein, that is, higher than the strength of the cover inner layer in itself by a value attributable to the protrusions of higher hardness. Then the cover inner layer exhibits a harder behavior, leading to an increased spin rate.
The golf ball comprising the cover inner and outer layers with the outer layer protrusions fitted in the inner layer recesses according to the invention

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