Multi-piece solid golf ball

Details Multi-piece solid golf ball Multi-piece solid golf ball

1999-09-03

2001-04-03

Graham, Mark S. (Department: 3711)

Games using tangible projectile

Golf

Ball

C473S376000

Reexamination Certificate

active

06210292

ABSTRACT:

This invention relates to a multi-piece solid golf ball comprising at least three layers, including a solid core, an intermediate layer, and a cover.
BACKGROUND OF THE INVENTION
Many two-piece solid golf balls are known in the art. As compared with wound golf balls, solid golf balls have the advantage of an increased total flight distance on both driver and iron shots, because of a straight liner trajectory and a low spin receptivity due to their structure, which allows for a long run. On the other hand, two-piece solid golf balls are more difficult to control than the wound golf balls in that they do not stop short on the green because of low spin receptivity on iron shots.
Like flight distance, a soft feel when hit is essential for golf balls. The absence of a soft feel represents a substantial loss of commodity value. As compared with the two-piece solid golf balls, the wound golf balls have the structural characteristics ensuring a soft and pleasant feel.
On two-piece solid golf balls consisting of a core and a cover, attempts have been made to soften the ball structure in order to accomplish a soft feel upon impact. A soft core is often used to obtain such soft-feel two-piece solid golf balls, but making the core softer lowers the resilience of the golf ball, compromises flight performance, and also markedly reduces durability. As a result, not only do these balls lack the excellent flight performance and durability characteristic of ordinary two-piece solid golf balls, but they are often in fact unfit for actual use.
Various three-piece solid golf balls having a three-layer construction in which an intermediate layer is situated between a solid core and a cover have been proposed to resolve these problems as disclosed, for example, in JP-A 7-24084, 6-23069, 4-244174, 9-10358, and 9-313643.
Golf balls having the cover and the intermediate layer made soft according to these proposals have a soft feel, but a shorter flight distance on full shots with a driver. To insure distance, the cover and the intermediate layer must be formed hard at the sacrifice of the feel upon approach shots and putting. Additionally, the spin performance on iron shots is also exacerbated so that the ball is less easy to control.
Numerous studies have been made on the dimples on the ball surface with respect to their shape (diameter and depth) and arrangement. It is difficult to optimize the dimples. Most golf balls suffer from the problem that they will sky high or drop upon full shots with a driver.
None of prior art solid golf balls fully meet the demands of players. A further improvement is thus desired.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to provide a multi-piece solid golf ball comprising at least three layers, a solid core, an intermediate layer, and a cover, which has a very soft pleasant feel upon approach shots and putting, ease of control upon iron shots, and a satisfactory trajectory and improved flight performance upon full shots with a driver.
The invention is directed to a multi-piece solid golf ball comprising a solid core, an intermediate layer of at least one layer around the core, and a cover of at least one layer around the intermediate layer, and having a plurality of dimples formed in the surface of the cover. The cover is formed of a cover stock composed mainly of a thermoplastic resin and has a Shore D hardness A, the intermediate layer has a Shore D hardness B, and the Shore D hardness A of the cover is at least 20 units higher than the Shore D hardness B of the intermediate layer. The product (AxB) of the Shore D hardness A of the cover multiplied by the Shore D hardness B of the intermediate layer and a dimple volume ratio V
R
(%) satisfy a specific requirement. The dimple volume ratio V
R
is the ratio of the sum Vs of volumes of dimple spaces each defined below a plane circumscribed by the dimple edge divided by the volume of an imaginary sphere given on the assumption that no dimples are on the golf ball surface, and is calculated according to the following equation:
V
R
⁡
(
%
)
=
Vs
4
3
⁢
π
⁢
 
⁢
R
3
×
100
wherein Vs is defined above and R is a ball radius. Namely, when the range of the product (AxB) is divided into sub-ranges, the value of V
R
should fall in a specific range for each of the sub-ranges of (AxB). Specifically, the product (AxB) and the dimple volume ratio V
R
(%) satisfy any one of the following relationships (1) to (6):
(1) V
R
is 0.79 to 1.15% when AxB is 150 to 500,
(2) V
R
is 0.78 to 1.14% when AxB is 500 to 1,000,
(3) V
R
is 0.77 to 1.13% when AxB is 1,000 to 1,500,
(4) V
R
is 0.76 to 1.12% when AxB is 1,500 to 2,000,
(5) V
R
is 0.75 to 1.11% when AxB is 2,000 to 2,500, and
(6) V
R
is 0.74 to 1.10% when AxB is at least 2,500.
The dimples include at least three types of dimples which are different in at least one of diameter, depth, and V
0
, which is the volume of a dimple space below a plane circumscribed by the dimple edge divided by the volume of a cylinder whose bottom is the plane and whose height is the maximum depth of the dimple from the bottom. Upon driver shots, the ball receives an optimum spin rate and thus travels a satisfactory trajectory.
In one preferred embodiment, the solid core is formed mainly of a rubber base and has a specific gravity of 1.0 to 1.5. The solid core is made relatively soft as demonstrated by a deflection of at least 2.5 mm under an applied load of 100 kg.
In a further preferred embodiment, the intermediate layer is formed mainly of a very soft thermoplastic resin as demonstrated by a Shore D hardness of 5 to 35. More preferably, the intermediate layer is formed mainly of a heated mixture of (E1) a thermoplastic polyester elastomer and (E2) at least one thermoplastic elastomer selected from olefin elastomers, modified olefin elastomers, styrene block copolymers and hydrogenated styrene block copolymers, or the thermoplastic elastomer defined as (E2).
In a still further preferred embodiment, the intermediate layer has a thickness of 0.2 to 5.0 mm and a specific gravity of at least 0.8: and the cover is formed mainly of an ionomer resin, especially having a Shore D hardness of 40 to 70, and has a thickness of 1.0 to 5.0 mm and a specific gravity of at least 0.9.
When all these features are fulfilled, the ball is given a very soft pleasant feel upon approach shots and putting, a high spin receptivity and hence, ease of control upon iron shots, and a satisfactory trajectory and improved flight performance upon full shots with a driver.


REFERENCES:
patent: 5556098 (1996-09-01), Higuchi et al.
patent: 244174 (1992-09-01), None
patent: 6-23069 (1994-02-01), None
patent: 7-24084 (1995-01-01), None
patent: 9-10358 (1997-01-01), None
patent: 09010358 (1997-01-01), None
patent: 9-313643 (1999-12-01), None

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