GOLF BALL

Information

  • Patent Application
  • 20170182373
  • Publication Number
    20170182373
  • Date Filed
    December 14, 2016
    8 years ago
  • Date Published
    June 29, 2017
    7 years ago
Abstract
A golf ball capable of reducing the moment of inertial while reducing spin in a driver shot will be provided. To that end, a golf ball of the disclosure is a golf ball having a cover and, provided that Ib (g·cm2) represents the moment of inertia of the golf ball, μ (mm) represents deflection hardness corresponding to a deformation amount (mm) of the golf ball in a load direction from when an initial load of 10 kgf is applied to the golf ball to when a final load of 130 kgf is applied to the golf ball, and D represents Shore D hardness of the cover, a spin change amount predictive index ΔS′ represented by the following formula:
Description
TECHNICAL FIELD

This disclosure concerns a golf ball.


BACKGROUND

In General, desirable performance of a golf ball (hereinafter, sometimes simply referred to as a “ball”) is such that the ball easily flies farther in a driver shot, while the ball easily stops in an approach shot. It has been known that, in order to obtain a ball that easily flies farther in a driver shot, the spin of the ball in a driver shot should be reduced, whereas, in order to obtain a ball that easily stops in an approach shot, the spin of the ball in an approach shot should be increased.


Conventionally, it had been believed that, in order to reduce the spin in a driver shot, it is effective to increase the moment of inertia of the ball, whereas, in order to increase the spin in an approach shot, it is effective to reduce the moment of inertia of the ball (e.g., PLT 1).


CITATION LIST
Patent Literature

PLT 1: JP-A-2014-110940


SUMMARY

We have found, however, that, by adjusting the structure of the ball appropriately, it is possible, even when the moment of inertia of the ball is small, to not only increase the spin in an approach shot, but also to reduce the spin in a driver shot.


It could be helpful to provide a golf ball capable of reducing the moment of inertia, while reducing the spin in a driver shot.


A golf ball of the disclosure is a golf ball provided with a cover, wherein,

    • provided that
      • Ib (g·cm2) represents a moment of inertia of the golf ball,
      • μ (mm) represents deflection hardness corresponding to a deformation amount (mm) of the golf ball in a load direction from when an initial load of 10 kgf is applied to the golf ball to when a final load of 130 kgf is applied to the golf ball, and
      • D represents Shore D hardness of the cover,
    • a spin change amount predictive index ΔS′ represented by the following formula:







Δ






S



=



(

μ
D

)

2





82
-

I
b



82
2


·

10
6







is at least 2.0.


The golf ball of the disclosure can reduce the moment of inertia, while reducing the spin in a driver shot.


The golf ball of the disclosure may be configured such that the cover is made of urethane.


According to this configuration, the spin in a driver shot can be further reduced.


The golf ball of the disclosure may be configured such that the spin change amount predictive index ΔS′ is at least 2.5.


According to this configuration, it is further possible to reduce the moment of inertia, while reducing the spin in a driver shot.


The golf ball of the disclosure may be configured such that the spin change amount predictive index ΔS′ is at least 3.0.


According to this configuration, it is further possible to reduce the moment of inertia, while reducing the spin in a driver shot.


The golf ball of the disclosure may be configured such that

    • the cover is coated with a top coat, and
    • an elastic work recovery rate of the top coat is 30 to 98%.


According to this configuration, the spin in a driver shot can be further reduced.


The golf ball of the disclosure may be configured such that

    • an outer surface of the cover has a plurality of dimples, and
    • provided that
      • PS7 represents an area of the golf ball in contact with a flat surface upon application of a load of 700 kgf to the golf ball against the flat surface, and
      • VS represents, assuming that the golf ball has no dimples on its surface, an area of a circle of a cross-section of the golf ball taken along a diameter of the golf ball,
    • the following formula:





(PS7/VS/μ)·100≧6.70(mm−1)


is satisfied.


According to this configuration, the spin in a driver shot can be further reduced.


According to the disclosure, a golf ball capable of reducing the moment of inertia, while reducing the spin in a driver shot, can be provided.





BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:



FIG. 1 is a cross-sectional diagram illustrating an example of an internal structure of a golf ball according to one embodiment of the disclosure;



FIGS. 2A and 2B are diagrams illustrating spins of the golf ball put in a driver shot: FIG. 2A is a schematic diagram illustrating a state of a driver shot, and FIG. 2B is a graph illustrating force acting between the golf ball and a golf club in a driver shot;



FIG. 3 is a diagram illustrating effects of the golf balls of the disclosure;



FIG. 4 is a diagram illustrating the effects of the golf balls of the disclosure;



FIGS. 5A to 5F are diagrams illustrating the effects of the golf balls of the disclosure;



FIGS. 6A to 6F are diagrams illustrating the effects of the golf balls of the disclosure;



FIGS. 7A and 7B are diagrams illustrating an example of dimples applicable to the golf ball of the disclosure: FIG. 7A is a side view of an example of the golf ball, and FIG. 7B is a cross-sectional view of a portion of the golf ball illustrated in FIG. 7A;



FIGS. 8A and 8B are diagrams illustrating another example of the dimples applicable to the golf ball of the disclosure: FIG. 8A is a side view of another example of the golf ball, and FIG. 8B is a cross-sectional view of a portion of the golf ball illustrated in FIG. 8A; and



FIGS. 9A and 9B are diagrams illustrating states of the same golf ball upon applications of respective loads of 6864 N and 1961 N thereto.





DETAILED DESCRIPTION

Hereinafter, embodiments of the disclosure will be described by way of example with reference to the drawings.


[Structure of Golf Ball of the Disclosure]


A golf ball according to one embodiment of the disclosure includes, for example, in addition to a core and an intermediate layer on an outer side of the core, a cover forming an outermost layer.



FIG. 1 is a cross-sectional view illustrating an example of an internal structure of the golf ball according to one embodiment of the disclosure. A golf ball 1 of an example of FIG. 1 is what is called a five-piece golf ball including an inner core 11, an intermediate core 12 provided on an outer side of the inner core 11, an outer core 13 provided on an outer side of the intermediate core 12, an intermediate layer 14 provided on an outer side of the outer core 13, and a cover 15 having a plurality of dimples 30 formed on an outer surface thereof and provided on an outer side of the intermediate layer 14. The cover 15 is coated with a top coat 16.


However, the golf ball of the disclosure can have any internal structure other than that of FIG. 1. For example, the core of the golf ball of the disclosure does not need to have a three-layer structure composed of the inner core 11, the intermediate core 12, and the outer core 13 as illustrated in the example of FIG. 1 but can have a structure composed of one layer, two layers, or 4 or more layers. Also, the intermediate layer of the golf ball of the disclosure can be composed of a plurality of layers.


According to the golf ball of the disclosure, provided that Ib (g·cm2) represents the moment of inertia of the ball, μ (mm) represents deflection hardness of the ball, and D represents Shore D hardness of the cover, a spin change amount predictive index ΔS' represented by the following formula:










Δ






S



=



(

μ
D

)

2





82
-

I
b



82
2


·

10
6







(
1
)







is at least 2.0 (ΔS′≧2.0).


Here, the moment of inertia of the ball (Ib) can be obtained by measurement using a moment of inertial measuring apparatus (for example, M01-005 manufactured inertia Dynamics, Inc.). This measuring apparatus calculates the moment of inertial of the golf ball from a difference between a period of vibration when the golf ball is placed on a jig of the measuring apparatus and a period of vibration when the golf ball is not placed.


The deflection hardness μ (mm) of the golf ball corresponds to a deformation amount (mm) of the golf ball in a load direction from when an initial load of 10 kgf (approx. 98 N) is applied to the golf ball to when a final load of 130 kgf (approx. 1275 N) is applied to the golf ball. The higher the value of the deflection hardness of the golf ball, the softer the golf ball.


The Shore D hardness (D) of the cover is a value obtained by preparing a sheet-like test piece with a thickness of 2 mm from a material of the cover and measuring hardness of the sheet-like test piece by using an ASTM-D2240 standard durometer “Type D”. The higher the value of the Shore D hardness of the cover, the harder the cover.


Note that, as can be seen from the formula (1), in order to have a positive value (larger than zero) of the spin change amount predictive index ΔS′, the moment of inertia of the golf ball Ib needs to be smaller than 82 g·cm2. The value 82 in formula (1) is being used based on the fact that the moment of inertia of existing common golf balls is approximately 81 to 82 g·cm2. That is, the moment of inertia of the golf ball of the disclosure is lower than that of the common golf balls.


Note that, hereinafter, the golf ball having the moment of inertia of 82 g·cm2 is referred to as a “standard ball.


Also, the golf ball of the disclosure satisfies ΔS′≧2.0 by having the following three factors being appropriately adjusted: the moment of inertia of the ball Ib, the deflection hardness of the ball, and the Shore D hardness of the cover.


The golf ball according to one embodiment of the disclosure satisfies weight (45.93 g or less) and an outer diameter (42.67 mm or more) prescribed by USGA and R&A.


As can be understood from the descriptions of Examples and Comparative Examples set forth below, the golf ball of the disclosure, as compared with the standard ball, can reduce the moment of inertia, while, not only increasing spin in an approach shot but also reducing spin in a driver shot.


[How we Obtained Formula for a Spin Change Amount Predictive Index ΔS′]


As described above, we have found that, depending on the structure of the ball, it is possible, even when the moment of inertia is small, to not only increase the spin in an approach shot but also to reduce the spin in a driver shot. We then conceived that the spin change amount predictive index ΔS′ defined by the formula (1) allows an evaluation of an actual spin change amount predictive index.


Here, how we obtained the spin change amount predictive index ΔS′ will be described with reference to FIGS. 2A and 2B. FIG. 2A is a schematic diagram illustrating a state of a driver shot, and FIG. 2B is a graph illustrating force acting between the golf ball 1 and a head 2 of a golf club and generated by a driver shot. In the graph of FIG. 2B, the horizontal axis represents time, and the vertical axis represents force exerted to the golf ball 1 from a club face 21 of the head 2 of the golf club. A “contact period” in FIG. 2B refers to a period in which the ball 1 is in contact with the club face 21. As for waveforms in FIG. 2B, a waveform of a solid line is a waveform of the force actually acting on the ball 1, and a sine-like wave, partially drawn with a broken line smoothly continuous from the waveform of the solid line, is provided to obtain a recoil period T described later.


As illustrated in FIGS. 2A and 2B, in a driver shot, the force (shear force) acting on the ball 1 from the club face 21 is generated first in a direction of putting a backspin on the ball 1 (in a positive direction) and, later, in a direction of putting a topspin, reverse to the backspin, on the ball 1 (in a negative direction). Here, provided that Fb represents a total sum of the force (impulse) acting on the ball 1 in the direction of putting the backspin while the club face 21 and the ball 1 are in contact with each other, and Ftop represents a total sum of the force (the impulse) generated in the direction of putting the topspin while the club face 21 and the ball 1 are in contact with each other (taking positive and negative signs into account), as the absolute value of the total thereof (Fback+ttop) becomes smaller, the spin amount of the spin put on the ball 1 by a driver shot decreases, hence it becomes more favorable.


In the graph of FIG. 2B, T representing the period of the waveform partially drawn with a broken line smoothly continuous from the waveform of the solid line (also referred to as the “recoil period”) is expressed by the following formula:









T
=

2


π
/




K
x

m

+


K
t

I









(
2
)







Here, Kx represents transverse rigidity of the ball, Kt represents rotational rigidity of the ball, m represents mass of the ball, and I represents the moment of inertia of the ball.


As a result of various experiments and analyses, we have found that:


(i) as the recoil period T becomes shorter, the total sum (Fback+Ftop) of the impulse of the force exerted on the ball 1 from the club face 21 becomes smaller, thus the spin amount decreases,


(ii) as the deflection hardness (pi) of the ball 1 becomes higher (i.e., as the ball becomes softer), the contact period of the club face 2 and the ball 1 becomes longer, and the total sum of the force (the impulse) Ftop generated in the direction of putting the topspin on the ball increases, and hence the spin amount decreases, and


(iii) as the Shore D hardness (D) of the cover of the ball 1 becomes smaller (i.e., as the cover becomes softer), the friction between the club face 2 and the ball 1 becomes higher, and the shear force exerted on the ball is generated earlier,


and also found the relationships between the points (i) to (iii). The points (ii) and (iii) can increase or decrease the effect of point (i). Based on these findings, we defined an index S for predicting the effect of the spin amounts in a driver shot and an approach shot from the structure of the golf ball as









S
=



μ
D

·


2

π

T


=


μ
D






K
x

m

+


K
t

I









(
3
)







The meaning of this spin amount predictive index S is such that, when ball structures of the same deflection hardness μ and the same Shore D hardness D are compared, where the moment of inertia I is a variable value, the larger the spin amount predictive index S, the less the spin amount in a driver shot.


In formula (3), when the moment of inertia of the ball is reduced as






I→I−ΔI,


a change amount ΔS of the spin predictive index S is










Δ





S

=





S



I



Δ





I

=





μ






K
t



2





D






K
x

m

+


K
t

I




·


Δ





I


I
2



=



K
t

2




(

μ
D

)

2



1
S




Δ





I


I
2









(
4
)







In formula (4), suppose





ΔI=Ia−Ib


is satisfied,










Δ





S

=



K
t

2




(

μ
D

)

2



1
S





I
a

-

I
b



I
a
2







(
5
)







is obtained. Here, Ia represents the moment of inertia of the standard ball, and Ib represents the moment of inertia of the ball subject to evaluation.


In formula (5), Kt and S are values associated with the standard ball and thus can be regarded as constant coefficients. For convenience, the constant coefficients in formula (5) are manipulated as shown in formula (6), whereby a spin change amount predictive index ΔS′ is defined by










Δ






S



=



2

K
t



S





Δ






S
·

10
6



=



(

μ
D

)

2



1
S






I
a

-

I
b



I
a
2


·

10
6








(
6
)







In formula (6), if the moment of inertia of the standard ball Ia is substituted by 82, the formula (1) set forth above can be obtained.


EXAMPLES AND COMPARATIVE EXAMPLES

As described above, the golf ball of the disclosure is configured such that ΔS′≧2.0 is satisfied by having the following three factors being appropriately adjusted: the moment of inertia of the ball (Ib), the deflection hardness (μ) of the ball, and the Shore D hardness (D) of the cover. With this configuration, as compared with the standard ball, the moment of inertia is reduced, while, not only increasing the spin in an approach shot, but also reducing the spin in a driver shot.


The golf balls of the disclosure according to Examples 1 to 13 and Comparative Examples 1 to 14 were prepared and evaluated. Results of the evaluation will be described with reference to Tables 1 to 5 and FIGS. 3 to 4. Details of Examples 1 to 13 are shown in Table 1, and details of Comparative Examples 1 to 14 are shown in Table 2.


In Table 1 and Table 2, lower case letters a to u shown in columns of “Composition” of the inner core 11, the intermediate core 12, and the outer core 13 correspond to compositions a to u in Table 3, respectively. In Table 1 and Table 2, also, upper case letters A to H shown in columns of “Composition” of the intermediate core 12, the outer core 13, the intermediate layer 14, and the cover 15 correspond to compositions A to H in Table 4, respectively. The numbers of compositions in Tables 3 and 4 are in unit of parts by weight.


In Tables 1 and 2, “μ: Deflection hardness (mm)” is the deformation amount (mm) of the respective balls in the load direction from when an initial load of 10 kgf (approx. 98 N) is applied to the ball to when a final load of 130 kgf (approx. 1275 N) is applied to the ball.


In Tables 1 and 2. “Ib: Moment of inertia (g·cm2)” is a value obtained by measuring the respective balls using a moment of inertia measuring apparatus (M01-005 manufactured inertia Dynamics, Inc.).


In Tables 1 and 2, “Shore D hardness” of the intermediate layer 14 and “D: Shore D hardness” of the cover 15 were obtained by preparing a sheet-like test piece with the thickness of 2 mm from respective materials and measuring the hardness of the test piece using an ASTM-D2240 standard durometer “Type D”.


In Tables 1 and 2, “ΔS′: Spin change amount predictive index” is a value calculated from the formula (1) set forth above by using values p, D, and Ib of the respective balls.


In Tables 1 and 2. “Driver spin (rpm)” and “Approach spin (rpm)” refer to results of experiments of the spin amounts that were obtained by a driver shot and an approach shot, respectively, using respective balls.


In experiments of driver shot, a driver (W#1) was attached to a Golf Swing Robot (manufactured by Miyamae Co., Ltd.), and the spin amount at the time when the robot hit the ball, with a head speed (HS) of 45 m/s, was measured. The golf club that was used for the experiments was “TourStage X-Drive 705 TYPE415 (2011 model)” (loft: 9.5°) manufactured by Bridgestone Sports Co., Ltd.


In experiments of approach shot, a sand wedge (SW) was attached to a Golf Swing Robot (manufactured by Miyamae Co., Ltd.), and the spin amount at the time when the robot hit the ball, with a head speed (HS) of 20 m/s, was measured. The golf club that was used for the experiments was “TourStage X-WEDGE” (loft: 56°) manufactured by Bridgestone Corporation.


The columns “Dimples”, “PS7: Pressured area”, “PS2: Pressured area”. “VS: Virtual area”, “(PS7/VS/μ)·100 (mm−1)”, “(PS2/VS/μ)·100 (mm−1)”, and “Top coat” in Tables 1 and 2 will be described later.























TABLE 1







Ex-
Ex-
Ex-
Ex-
Ex-
Ex-
Ex-
Ex-
Ex-
Ex-
Ex-
Ex-
Ex-




ample
ample
ample
ample
ample
ample
ample
ample
ample
ample
ample
ample
ample




1
2
3
4
5
6
7
8
9
10
11
12
13





























Inner
Diameter (mm)
18.1
18.1
18.1
18.1
18.1
18.1
18.1
18.1
18.1
18.1
18.1
18.1
18.1


core
Specific gravity
2.85
2.85
2.85
1.78
1.78
2.85
2.85
2.85
2.85
2.85
2.85
2.85
2.85



Composition
d
e
f
h
i
e
f
d
e
f
d
e
f


Inter-
Diameter (mm)
29
29
29


29
29
29
29
29
29
29
29


mediate
Specific gravity
0.96
0.96
0.96


0.96
0.96
0.96
0.96
0.96
0.96
0.96
0.96


core
Composition
E
F
G


F
G
E
F
G
E
F
G


Outer
Diamter (mm)
37.7
37.7
37.7
37.7
37.7
37.7
37.7
37.7
37.7
37.7
37.7
37.7
37.7


core
Specific gravity
0.96
0.96
0.96
1.1
1.1
0.96
0.96
0.96
0.96
0.96
0.96
0.96
0.96



Composition
D
E
H
k
l
E
H
D
E
H
D
E
H


Inter-
Diameter (mm)
41.05
41.05
41.05
41.05
41.05
41.05
41.05
41.05
41.05
41.05
41.05
41.05
41.05


mediate
Specific gravity
0.96
0.96
0.96
0.96
0.96
0.96
0.96
0.96
0.96
0.96
0.96
0.96
0.96


layer
Shore D
62
62
62
62
62
62
62
62
62
62
62
62
62



hardness
















Composition
CI
CI
CI
CI
CI
CI
CI
CI
CI
CI
CI
CI
CI


Cover
Diameter (mm)
42.7
42.7
42.7
42.7
42.7
42.7
42.7
42.7
42.7
42.7
42.7
42.7
42.7



Specific gravity
1.15
1.15
1.15
1.15
1.15
1.15
1.15
1.15
1.15
1.15
1.15
1.15
1.15



D: Shore D
47
47
47
47
47
61
61
47
47
47
47
47
47



hardness
















Composition
A
A
A
A
A
B
B
A
A
A
A
A
A




















μ: Deflection
2.5
3.0
3.5
3.0
3.5
2.8
3.3
2.5
3.0
3.5
2.5
3.0
3.5


hardness (mm)















Ib: Moment of
74.5
74.5
74.5
78.7
78.7
74.5
74.5
74.5
74.5
74.5
74.5
74.5
74.5


inertia (g · cm2)















Dimples
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.



7A
7A
7A
7A
7A
7A
7A
7A
7A
7A
8A
8A
8A



and 7B
and 7B
and 7B
and 7B
and 7B
and 7B
and 7B
and 7B
and 7B
and 7B
and 8B
and 8B
and 8B


PS7: pressured area
225
265
297
268
301
252
284
222
269
290
282
329
365


PS2: pressured area
64
72
89
74
92
70
84
62
76
90
75
91
100


VS: virtual area
1432
1432
1432
1432
1432
1432
1432
1432
1432
1432
1432
1432
1432


(PS7/VS/μ) · 100 (mm−1)
6.28
6.17
5.93
6.24
6.01
6.28
6.01
6.20
6.26
5.79
7.88
7.66
7.28


(PS7/VS/μ) · 100 (mm−1)
1.79
1.68
1.78
1.72
1.84
1.75
1.78
1.73
1.77
1.80
20.9
2.12
2.00





















Top
Composition
I
I
I
I
I
I
I
J
J
J
I
I
I


Coat
Film thickness
15
15
15
15
15
15
15
15
15
15
15
15
15



(μm)
















Elastic work
16.3
16.3
16.3
16.3
16.3
16.3
16.3
80.1
80.1
80.1
16.3
16.3
16.3



recovery
















rate (%)

































ΔStext missing or illegible when filed : Spin change
3.2
4.5
6.2
2.0
2.7
2.4
3.3
3.2
4.5
6.2
3.2
4.5
6.2


amount















predictive index















Driver spin (rpm)
2821
2665
2515
2858
2674
2639
2445
2805
2654
2527
2811
2651
2518


Approach spin (rpm)
6319
6169
6019
6063
5856
5819
5669
6332
6194
6034
6341
6197
6043






text missing or illegible when filed indicates data missing or illegible when filed





























TABLE 2







Compar-
Compar-
Compar-
Compar-
Compar-
Compar-
Compar-
Compar-
Compar-
Compar-
Compar-
Compar-
Compar-
Compar-




ative
ative
ative
ative
ative
ative
ative
ative
ative
ative
ative
ative
ative
ative




Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example
Example




1
2
3
4
5
6
7
8
9
10
11
12
13
14






























Inner
Diameter (mm)
18.1
18.1
18.1



18.1
18.1
18.1
18.1



18.1


core
Specific gravity
1.4
1.4
1.4



1.78
1.4
1.4
1.4



2.85



Composition
p
q
r



g
p
q
r



d


Inter-
Diameter (mm)
















mediate
Specific gravity
















core
Composition
















Outer
Diamter (mm)
37.7
37.7
37.7
37.7
37.7
37.7
37.7
37.7
37.7
37.7
37.7
37.7
37.7
37.7


core
Specific gravity
1.14
1.14
1.14
1.17
1.17
1.17
1.1
1.14
1.14
1.14
1.17
1.17
1.17
0.96



Composition
s
t
u
a
b
c
j
s
t
u
m
n
o
D


Inter-
Diameter (mm)
41.05
41.05
41.05
41.05
41.05
41.05
41.05
41.05
41.05
41.05
41.05
41.05
41.05
41.05


mediate
Specific gravity
0.96
0.96
0.96
1.0
1.0
1.0
0.96
0.96
0.96
0.96
1.0
1.0
1.0
0.96


layer
Shore D
62
62
62
62
62
62
62
62
62
62
62
62
62
62



hardness

















Composition
C1
C1
C1
C2
C2
C2
C1
C1
C1
C1
C2
C2
C2
C2


Cover
Diameter (mm)
42.7
42.7
42.7
42.7
42.7
42.7
42.7
42.7
42.7
42.7
42.7
42.7
42.7
42.7



Specific gravity
1.15
1.15
1.15
1.15
1.15
1.15
1.15
1.15
1.15
1.15
1.15
1.15
1.15
1.16



D: Shore D
47
47
47
47
47
47
47
61
61
61
61
61
61
61



hardness

















Composition
A
A
A
A
A
A
A
B
B
B
B
B
B
B





















μ: Deflection
2.5
3.0
3.5
2.5
3.0
3.5
2.5
2.3
2.8
3.3
2.3
2.8
3.3
2.3


hardness (mm)
















Ib: Moment of
80
80
80
82
82
82
78.7
80
80
80
82
82
82
74.5


inertia (g · cm2)
















Dimples
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
FIGS.
























7A
7A
7A
7A
7A
7A
7A
7A
7A
7A
7A
7A
7A
7A




and 7B
and 7B
and 7B
and 7B
and 7B
and 7B
and 7B
and 7B
and 7B
and 7B
and 7B
and 7B
and 7B
and 7B





















PS7: pressured area
224
267
301
222
260
295
221
211
250
285
223
261
292
220


PS2: pressured area
63
75
93
63
70
86
62
56
72
83
64
71
85
63


VS: virtual area
1432
1432
1432
1432
1432
1432
1432
1432
1432
1432
1432
1432
1432
1432


(PS7/VS/μ) · 100 (mm−1)
6.26
6.22
6.01
6.20
6.05
5.89
6.17
6.41
6.24
6.03
6.77
6.51
6.18
6.68


(PS7/VS/μ) · 100 (mm−1)
1.76
1.75
1.86
1.76
1.63
1.72
1.73
1.70
1.80
1.76
1.94
1.77
1.80
1.91






















Top
Composition
I
I
I
I
I
I
I
I
I
I
I
I
I
I


Coat
Film thickness
15
15
15
15
15
15
15
15
15
15
15
15
15
15



(μm)

















Elastic work
16.3
16.3
16.3
16.3
16.3
16.3
16.3
16.3
16.3
16.3
16.3
16.3
16.3
16.3



recovery

















rate (%)



































ΔStext missing or illegible when filed : Spin change amount
0.8
1.2
1.6
0
0
0
1.4
0.4
0.6
0.9
0
0
0
1.6


predictive index
















Driver spin (rpm)
3102
2941
2779
3079
2919
2759
3142
2898
2740
2579
2879
2719
2559
2913


Approach spin (rpm)
6201
6023
5836
6155
5986
5816
6251
5883
5692
5486
5805
5636
5466
5969






text missing or illegible when filed indicates data missing or illegible when filed


























TABLE 3








Compo-
Compo-
Compo-
Compo-
Compo-
Compo-
Compo-
Compo-
Compo-
Compo-
Compo-
Compo-



sition
sition
sition
sition
sition
sition
sition
sition
sition
sition
sition
sition



a
b
c
d
e
f
g
h
i
j
k
l





Polybtext missing or illegible when filed
100
100
100
100
100
100
100
100
100
100
100
100


Zinc
27.0
23.0
19.0
20.0
17.0
14.0
20.0
17.0
14.0
27.0
23.0
19.0


acrylate














Peroxide *1
3
3
3
3
3
3
3
3
3
3
3
3


Tungsten
0
0
0
268
266
264
102
101.8
101.6
0
0
0


Anti-aging
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1


agent *2














Zinc oxide
21.0
22.5
24.0
5.0
5.0
5.0
5.
5.0
5.0
10.0
11.5
13.5






















Compo-
Compo-
Compo-
Compo-
Compo-
Compo-
Compo-
Compo-
Compo-




sition
sition
sition
sition
sition
sition
sition
sition
sition




m
n
o
p
q
r
s
t
u






Polybtext missing or illegible when filed
100
100
100
100
100
100
100
100
100



Zinc
25.5
21.5
17.5
20.0
17.0
14.0
27.0
23.0
19.0



acrylate












Peroxide *1
3
3
3
3
3
3
3
3
3



Tungsten
0
0
0
48
48.5
49
0
0
0



Anti-aging
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1



agent *2












Zinc oxide
22.0
23.5
25.0
5.0
5.0
5.0
8.0
10.0
12.0





*1 Peroxide(2): Mixture of 1,1-Di(t-butylperoxy)cyclohexane and silica, product name PERtext missing or illegible when filed  (product of NOF Corporation)


*2 Anti-aging agent: product name Notext missing or illegible when filed  NS-6 (product of Ouchi Shinko Chemical Industrial Co. Ltd)



text missing or illegible when filed indicates data missing or illegible when filed























TABLE 4






Compo-
Compo-
Compo-
Compo-
Compo-
Compo-
Compo-
Compo-
Compo-



sition
sition
sition
sition
sition
sition
sition
sition
sition



A
B
C1
C2
D
E
F
G
H
























T-8290
75










T-8283
25










T-8260

100









Himilan 1706


35
35







Himilan 1557


15
15







Himilan 1605


50
50







HPF1000




100






HPF2000





100


50


AD1035






100

50


AD1172







100



Hytrel 4001
11
11









Titanium oxide
3.9
3

7







Polyethylene
1.2
1









wax











Isocyanate
7.5
7.5









compound











Trimethylol-


1.1
1.1







propane


















The following are details of materials in Table 4.


T-8290: PANDEX® produced by DIC Bayer Polymer Ltd., MDI-PTMG-type thermoplastic polyurethane


T-8283: PANDEX®@ produced by DIC Bayer Polymer Ltd., MDI-PTMG-type thermoplastic polyurethane


T-8260: PANDEX® produced by DIC Bayer Polymer Ltd., MDI-PTMG-type thermoplastic polyurethane


Himilan 1706: ionomer produced by Du Pont-Mitsui Polychemicals Co., Ltd.


Himilan 1557: ionomer produced by Du Pont-Mitsui Polychemicals Co., Ltd.


Himilan 1605: ionomer produced by Du Pont-Mitsui Polychemicals Co., Ltd.


HPF1000: Dupont HPF


HPF2000: Dupont HPF


AD1035: Dupont HPF


AD1172: Dupont HPF


Hytrel 4001: thermoplastic polyether-ester elastomer produced by Du Pont-Toray Co., Ltd.


Polyethylene wax: “SANWAX161P” (product of Sanyo Chemical Industries, Ltd.)


Isocyanate composition: 4,4′-diphenylmethane diisocyanate


*Note that C1 and C2 have equivalent physical property values, and differ only in specific gravity.



FIG. 3 is a diagram illustrating the driver spin (rpm) and the approach spin (rpm) of the balls of the Examples 1 to 5 and Comparative Examples 1 to 7, the covers 15 of which have the Shore D hardness (D) of 47. FIG. 4 is a diagram illustrating the driver spin (rpm) and the approach spin (rpm) of the balls of the Examples 6 to 7 and Comparative Examples 8 to 14, the covers 15 of which have the Shore D hardness (D) of 61. In FIG. 3 and FIG. 4, the horizontal axis represents the driver spin (rpm), and the vertical axis represents the approach spin (rpm). As described above, it is desirable when the spin amount is small in a driver shot and when the spin amount is large in an approach shot. Therefore, in FIG. 3 and FIG. 4, performance of the ball becomes more favorable while moving from the lower right towards the upper left.


As can be seen in FIG. 3 and FIG. 4, when comparing the balls of the Comparative Examples and Examples which have the covers 15 of the same Shore D hardness (D), the balls of the Examples which satisfied ΔS′≧2.0, as compared with the balls of the Comparative Examples, favorably achieved both increase of the spin amount in an approach shot and reduction of the spin amount in a driver shot.



FIGS. 5A to 5F each illustrate the driver spin (rpm) of the balls of the Comparative Examples and Examples which have the covers 15 of the same Shore D hardness (D) and deflection hardness (μ). FIGS. 6A to 6F each illustrate the approach spin (rpm) of the balls of the Comparative Examples and Examples which have the covers 15 of the same Shore D hardness (D) and deflection hardness (p).


As can be seen in FIGS. 5A to 5F and FIGS. 6A to 6F, when comparing the balls of the Comparative Examples and Examples which have the covers 15 of the same Shore D hardness (D) and deflection hardness (pi), the balls of the Examples which satisfied ΔS′≧2.0, as compared with the balls of the Comparative Examples, favorably achieved reduction of the spin amount in a driver shot or increase of the spin amount in an approach shot.


Note that, from the viewpoint of reducing the moment of inertia of the ball while reducing the spin amount of a driver shot, the ball 1 of the present embodiment has the spin change amount predictive index ΔS′ of preferably at least 2.5, more preferably at least 3.0.


From a similar viewpoint, the ball 1 of the present embodiment preferably satisfies Ib≦80 g·cm2, 2.0 mm≦μ≦4.5 mm, and D≦65. More preferably, the ball 1 of the present embodiment satisfies 72 g·cm2≦Ib≦79 g·cm2, 2.5 mm≦μ≦3.0 mm, and D≦55.


The cover 15 of the ball 1 of the present embodiment is preferably made of urethane. Therein a driver shot, the frictional force between the ball 1 and the club face 21 of the golf club can be increased, hence the spin amount can be further reduced.


[Dimples]


Next, the dimples 30 of the ball 1 of the present embodiment will be described in more detail. The dimples 30 of the ball 1 of the present embodiment can have any shape. FIGS. 7A to 7B and FIGS. 8A to 8B illustrate different examples of the dimples applicable to the ball 1 of the present embodiment.


In the example illustrated in FIGS. 7A to 7B, each dimple 30 is curved in a convex shape protruding toward the inside of the golf ball.


In the example illustrated in FIGS. 8A to 8B, the bottom surface of each of the dimples 30, only in the central area thereof, has a shape protruding toward the outside of the golf ball. In this case, without compromising original aerodynamic performance of the dimples 30, the pressured area, which will be described later, can be enhanced. Note that, as illustrated in FIG. 8B, the portion protruding toward the outside of the ball 1 in the central area of the dimples 30 may have a flat shape in the further central region of the central area. In this case, as illustrated in FIG. 8B, the peripheral portion of the flat region may have a chamfered (rounded) corner, whereby the contact area between the ball and the club face 21 at the time when the ball is hit can be increased, and hence the spin amount in a driver shot can be reduced.


Here, the ball 1 of the present embodiment preferably satisfies:





(PS7/VS/μ)·100≧5.70(mm−1)  (7)


In formula (7), “PS7” represents an area (referred to as the “pressured area”) (mm2) of the golf ball contacting with a flat surface when a load of 700 kgf (approx. 6864 N) is applied to the golf ball against the flat surface. In formula (7), “VS” represents an area (referred to as a “virtual plane area”) (mm2) of the circle of the cross-section of the golf ball taken along the diameter of the golf ball, when it is assumed that the golf ball has no dimples 30 on its surface. In formula (7). “μ” represents the deflection hardness (mm) of the ball 1 described above.


Note that “PS7/VS/μ” in formula (7) is synonymous with “PS7/(VS·μ)”. That is, “μ” in formula (7) is a variable of the denominator.


When the pressured area PS7 of the golf ball upon application of the load in a driver shot by a typical golfer satisfies the above formula (7), the contact area between the ball 1 and the club face 21 of the golf club increases and, simultaneously, the frictional force between the ball 1 and the club face 21 is enhanced. As a result, the backspin amount in a driver shot can be reduced, and hence the fly distance can be improved.


Note that, from a similar viewpoint, the ball 1 of the present embodiment more preferably satisfies the following formula:





(PS7/VS/μ)·100≧6.70(mm−1)  (8)


Also, the ball 1 of the present embodiment preferably satisfies the following formula:





(PS2/VS/μ)·100≧1.70(mm−1)  (9)


In formula (9), “PS2” is the area (referred to as the “pressured area”) (mm2) of the golf ball contacting with a flat surface when a load of 200 kgf (approx. 1961 N) is applied to the golf ball against the flat surface. VS and p are the same as those of the formulas (7) and (8).


Note that “PS2/VS/μ” in formula (9) is synonymous with “PS2/(VS·μ)”. That is, “μ” in formula (9) is a variable of the denominator.


When the pressured area PS2 of the golf ball upon application of the load in an approach shot by a typical golfer satisfies the above formula (9), the contact area between the ball 1 and the club face 21 of the golf club increases and, simultaneously, the frictional force between the ball 1 and the club face 21 is enhanced. Therefore, the backspin amount in an approach shot can be increased, and hence the ball 1 can stop sooner near its falling point.


Also, when the above formula (9) is satisfied, the total sum of the impulse (Fback+Ftop) of the force exerted on the ball 1 from the club face 21 in a driver shot becomes smaller and, simultaneously, the contact period of the club face 2 and the ball 1 becomes longer. Therefore, the total (the impulse) of the force generated in the direction of putting the top spin on the ball is increased, thereby the spin amount can be further reduced.


Note that, from a similar viewpoint, the ball 1 of the present embodiment more preferably satisfies the following formula:





(PS2/VS/μ)·100≧1.90(mm−1)  (10)


In reference to Tables 1 and 2, the balls of the Examples 1 to 10 and Comparative Examples 1 to 14 had the dimples 30 in the shape illustrated in FIGS. 7A and 7B, and the balls of the Examples 11 to 13 had the dimples 30 in the shape illustrated in FIGS. 8A and 8B.


The balls of the Examples 1 to 10 and Comparative Examples 1 to 14 each had the dimples 30 of six types with different diameters, out of which the dimples 30 with a typical diameter of 4.4 mm, as illustrated in FIG. 7B, had a depth L of 0.150 mm at its deepest point.


The balls of the Examples 11 to 13 had the dimples 30 of six types with different diameters, out of which the dimples 30 with a typical diameter of 4.4 mm, as illustrated in FIG. 8B, had a depth H of 0.097 mm at its central point C, a depth D of 0.131 mm at its deepest point, and, provided that a distance L1 along a virtual extension plane (a chain double-dashed line in FIG. 8B) of the peripheral surface of the ball 1 from the peripheral edge E to the central point C is 100, a distance L2 along the virtual extension plane of the peripheral surface of the ball 1 from the peripheral edge E to an adjacent deepest position was 39. Further, the dimples 30 with the typical diameter of 4.4 mm had a radius of curvature R of 0.5 mm and an edge angle A2 of 10.5°.


In Tables 1 and 2, the pressured areas PS7 and PS2 of each ball were measured by the following method. First, a pressure-sensitive sheet (a pressure measuring film, PRESCALE for medium pressure produced by Fujifilm Corporation) was placed on a flat surface, and the golf balls of the Examples and Comparative Examples were placed thereon. Then, by using Model 4204 produced instron Corporation, the load of 700 kgf (approx. 6864 N) and the load of 200 kgf (approx. 1961 N) were separately applied to the golf balls, and then the total area where the pressure-sensitive sheet developed color due to contact with the golf ball was measured by using PRESCALE pressure image analysis system FPD-9270 (product of Fujifilm Corporation). The pressured areas PS7 and PS2 in Tables 1 and 2 indicate results of the measurement conducted on a random portion of the golf ball.



FIG. 9A illustrates an example of an actual pressure-sensitive sheet which developed color upon application of the load of 700 kgf (approx. 6864 N) to the golf ball, and FIG. 9B illustrates an example of an actual pressure-sensitive sheet which developed color upon application of the load of 200 kgf (approx. 1961 N) to the same golf ball as that of FIG. 9A. In these figures, the circle portions are the dimples 30, and the colored area is where the color was developed.


[Top Coat]


Next, the top coat 16 coated on the cover 15 of the ball 1 of the present embodiment will be described in more detail. For the ball 1 of the present embodiment, the method of forming the top coat 16 (a coating layer) by coating the outer surface of the cover 15 with a coating material may be any method including, for example, an air gun coating method, an electrostatic coating method, and the like.


The thickness of the top coat 16 is not particularly limited but is normally 8 to 22 μm, preferably 10 to 20 μm.


The top coat 16 preferably has an “elastic work recovery rate”, which will be described later, of 30 to 98%, more preferably 70 to 90%. When the elastic work recovery rate of the top coat 16 is within the above ranges, the coating film formed on the surface of the golf ball has higher self-repair-and-recovery function while maintaining constant hardness and elasticity, thereby contributing to excellent durability and abrasion resistance of the ball. However, when the elastic work recovery rate of the top coat 16 deviates from the above ranges, there is a risk that sufficient approach spin may not be obtained.


The elastic work recovery rate of the top coat 16 is one of parameters of a nanoindentation method, which is used for evaluating physical properties of a coating film, and which is an ultra-micro hardness testing method where indentation load is controlled in the order of micronewton (μm) and the depth of an indenter at the time of indentation is tracked with the accuracy of nanometer (nm). Although the conventional method could only measure the size of a deformation mark (a plastic deformation mark) corresponding to the maximum load, the nanoindentation method can obtain a relationship between the indentation load and the indentation depth by automatic and continuous measurement. Therefore, unlike the conventional method, there is no individual differences in visual measurement of the deformation mark using an optical microscope, and hence the nanoindentation method is considered to be able to reliably and highly accurately evaluate the physical properties of a coating film. Accordingly, since the coating film on the surface of the golf ball can be greatly affected by the hitting by the driver or various golf clubs and can have more than little influence on various physical properties of the golf ball, measuring the coating film of the golf ball more accurately than the conventionally by using the ultra-micro hardness testing method enables a very effective evaluation.


For the balls of the Examples and Comparative Examples shown in Table 1 and 2, on the outer surface of the cover 15 (the outermost layver) having numerous dimples 30 formed thereon, the coating material was painted with an air spray gun so as to form the top coat 16 with a thickness of 15 μm. In Tables 1 and 2, alphabets I and J in columns of the “Composition” of the top coat 16 correspond to Composition I and Composition J in the following Table 5, respectively.











TABLE 5





Costing composition (parts by mass)
Composition I
Composition J


















Main
Polyol (1)
100.0



agent
Polyol (2)

100.0



Ethyl acetate
100.0
60.0



Propylene glycol
40.0
40.0



monomethyl





ester acetate





Curing catalyst
0.03
0.03


Curing
Nurate body of
30.5
52.5


agent
hexamethylene





diisocyanate (1)





Modified polyster of
46.8




hexamethylene





diisocyanate (2)





Ethyl acetate
42.7
47.5









Mixing molar ratio (NCO/OH)
1.08
1.08





*Coating composition A (molar ratio of NCO)


***Nurate body of hexamethylene diisocyanate (1): Modified polyester of hexamethylene diisocyanate (2) = 0.79:0.29.






Here, synthesis examples of acrylic polyol (1) and (2) in Table 5 will be described. Note that, in the following description, “parts” means “parts by mass”.


Synthesis Example 1 of Acrylic Polyol

Into a reactor vessel equipped with a stirrer, a thermometer, a cooling pipe, a nitrogen gas introducing pipe, and a dropping device, 1000 parts of butyl acetate was introduced and, while being stirred, heated to 100° C. Into thus obtained butyl acetate, a mixture of 220 parts of acrylic monomer containing polyester (PLACCEL FM-3 produced by Daicel Chemical Industries, Ltd.), 610 parts of methyl methacrylate, 170 parts of 2-hydroxyethyl methacrylate, and 30 parts of 2,2′-azobisisobutyronitrile was dropped over the period of 4 hours. After the dropping, a mixture thus obtained was left to react at the same temperature for 6 hours. After the reaction, 180 parts of butyl acetate and 150 parts of polycaprolactone diol (PLACCEL L205AL produced by Daicel Chemical Industries, Ltd.) were introduced into a resulting mixture and mixed. Thereby, transparent acrylic polyol resin solution (Polyol (1) in Table 5) with 50% solid content, viscosity of 100 mPa·s (25° C.), weight average molecular weight of 10,000, and a hydroxyl value of 113 mgKOH/g (solid content) was obtained.


Synthesis Example 2 of Acrylic Polyol

Into a reactor vessel equipped with a stirrer, a thermometer, a cooling pipe, a nitrogen gas introducing pipe, and a dropping device, 1000 parts of butyl acetate was introduced and, while being stirred, heated to 100° C. Into thus obtained butyl acetate, a mixture of 620 parts of acrylic monomer containing polyester (PLACCEL FM-3 produced by Daicel Chemical Industries, Ltd.), 317 parts of methyl methacrylate, 63 parts of 2-hydroxyethyl methacrylate, and 12 parts of 2.2′-azobisisobutyronitrile was dropped over the period of 4 hours. After the dropping, a mixture thus obtained was left to react at the same temperature for 6 hours. After the reaction, 532 parts of butyl acetate and 520 parts of polycaprolactone diol (PLACCEL L205AL produced by Daicel Chemical Industries, Ltd.) were introduced into a resulting mixture and mixed. Thereby, transparent acrylic polyol resin solution (Polyol (2) in Table 5) with 50% solid content, viscosity of 60 mPa·s (25° C.), weight average molecular weight of 70,000, and ahydroxyl value of 142 mgKOH/g (solid content) was obtained.


The elastic work recovery rate of the top coat 16 of the ball 1 of the Examples and Comparative Examples in Tables 1 and 2 was measured as follows. First, from the coating material used for the top coat 16, a coating film sheet with a thickness of 100 μm was prepared. Then, by using an ultra-micro hardness tester “ENT-2100” produced by ELIONIX Inc., the elastic work recovery rate was measured under the following condition.

    • Indenter: Berkovich indenter (material: diamond, angle α: 65.03°)
    • Load F: 0.2 mN
    • Loading period: 10 seconds
    • Maintaining period: 1 second
    • Unloading period: 1 second


Note that, based on an indention work amount Welast (Nm) due to a restoring deformation of the coating film and a mechanical indention work amount Wtotal (Nm), the elastic work recovery rate can be calculated from the following equation.





Elastic work recovery rate=(Welast/Wtotal)·100(%)  (11)

Claims
  • 1. A golf ball having a cover, wherein, provided that Ib (g·cm2) represents a moment of inertia of the golf ball,μ (mm) represents deflection hardness corresponding to a deformation amount (mm) of the golf ball in a load direction from when an initial load of 10 kgf is applied to the golf ball to when a final load of 130 kgf is applied to the golf ball, andD represents Shore D hardness of the cover,a spin change amount predictive index ΔS′ represented by the following formula:
  • 2. The golf ball according to claim 1, wherein the cover is made of urethane.
  • 3. The golf ball according to claim 1, wherein the spin change amount predictive index ΔS′ is at least 2.5.
  • 4. The golf ball according to claim 1, wherein the spin change amount predictive index ΔS′ is at least 3.0.
  • 5. The golf ball according to claim 1, wherein the cover is coated with a top coat, andan elastic work recovery rate of the top coat is 30 to 98%.
  • 6. The golf ball according to claim 1, wherein an outer surface of the cover has a plurality of dimples, andprovided that PS7 represents an area of the golf ball in contact with a flat surface upon application of a load of 700 kgf to the golf ball against the flat surface, andVS represents, assuming that the golf ball has no dimples on its surface, an area of a circle of a cross-section of the golf ball taken along a diameter of the golf ball,the following formula: (PS7/VS/μ)·100≧6.70(mm−1)
Priority Claims (1)
Number Date Country Kind
2015-252076 Dec 2015 JP national