U.S. patent application number 13/074240 was filed with the patent office on 2012-06-21 for multi-piece solid golf ball.
This patent application is currently assigned to BRIDGESTONE SPORTS CO., LTD.. Invention is credited to Akira KIMURA.
Application Number | 20120157235 13/074240 |
Document ID | / |
Family ID | 46235101 |
Filed Date | 2012-06-21 |
United States Patent
Application |
20120157235 |
Kind Code |
A1 |
KIMURA; Akira |
June 21, 2012 |
MULTI-PIECE SOLID GOLF BALL
Abstract
A multi-piece solid golf ball has a core, at least one
intermediate layer encasing the core, and a cover of at least one
layer encasing the intermediate layer. The core is formed of a base
rubber, and the intermediate layer and cover are each formed of a
resin material. The intermediate layer has a thickness (a) and the
cover has a thickness (b) such that the ratio a/b is from 0.7 to
1.9, and the core has a diameter (c) such that the ratio c/a with
the intermediate layer thickness (a) is from 23 to 38. The
intermediate layer has a material hardness (Shore D) of from 42 to
76, and the cover has a material hardness (Shore D) of from 41 to
69. The ball satisfies the following relationship: cover material
hardness<intermediate layer material hardness>core surface
hardness, and wherein a Shore D hardness at the core surface minus
a Shore D hardness at the core center is not more than 17 units.
This golf ball has an improved flight performance and a good, solid
feel on impact.
Inventors: |
KIMURA; Akira; (Chichibushi,
JP) |
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
Tokyo
JP
|
Family ID: |
46235101 |
Appl. No.: |
13/074240 |
Filed: |
March 29, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12975018 |
Dec 21, 2010 |
|
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13074240 |
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Current U.S.
Class: |
473/374 ;
473/378; 473/383; 473/384 |
Current CPC
Class: |
A63B 37/0043 20130101;
A63B 37/0096 20130101; A63B 37/0075 20130101; A63B 37/0045
20130101; A63B 37/0087 20130101; A63B 37/0065 20130101; A63B 37/002
20130101; A63B 37/0018 20130101; A63B 37/0064 20130101; A63B
37/0031 20130101; A63B 37/0033 20130101; A63B 37/0062 20130101;
A63B 37/0021 20130101; A63B 37/0019 20130101 |
Class at
Publication: |
473/374 ;
473/378; 473/383; 473/384 |
International
Class: |
A63B 37/06 20060101
A63B037/06; A63B 37/14 20060101 A63B037/14; A63B 37/12 20060101
A63B037/12 |
Claims
1. A multi-piece solid golf ball comprising a core, at least one
intermediate layer encasing the core, and a cover of at least one
layer encasing the intermediate layer, wherein the core is formed
of a base rubber, the intermediate layer and cover are each formed
of a resin material, the intermediate layer has a thickness (a) and
the cover has a thickness (b) such that the ratio a/b is from 0.7
to 1.9, the core has a diameter (c) such that the ratio c/a with
the intermediate layer thickness (a) is from 23 to 38, the
intermediate layer has a material hardness (Shore D) of from 42 to
76, the cover has a material hardness (Shore D) of from 41 to 69,
and the ball satisfies the following relationship: cover material
hardness<intermediate layer material hardness>core surface
hardness, and wherein a Shore D hardness at the core surface minus
a Shore D hardness at the core center is not more than 17
units.
2. The multi-piece solid golf ball of claim 1 wherein, letting the
ball deflection (mm) when compressed under a final load of 490 N
(50 kgf) from an initial load state of 98 N (10 kgf) be A and
letting the ball deflection (mm) when compressed under a final load
of 5,880 N (600 kgf) from an initial load state of 98 N (10 kgf) be
B, the value of B/A.times.100 is from 830 to 930.
3. The multi-piece solid golf ball of claim 1, wherein the ball
deflection B is from 7.0 to 10.0 mm, and the core deflection when
compressed under a final load of 1,275 N (130 kgf) from an initial
load state of 98 N (10 kgf) is from 2.1 to 4.1 mm.
4. The multi-piece solid golf ball of claim 1, wherein the resin
material of the cover is formed by injection molding a single resin
blend composed primarily of (A) a thermoplastic polyurethane and
(B) a polyisocyanate compound, which resin blend includes a
polyisocyanate compound in at least some portion of which all the
isocyanate groups on the molecule remain in an unreacted state.
5. The multi-piece solid golf ball of claim 1, wherein a plurality
of dimples are formed on a surface of the ball, the total number of
dimples is from 250 to 350, the dimples have a surface coverage
(SR) of at least 75%, and the ball, when hit, has a coefficient of
lift CL at a Reynolds number of 70,000 and a spin rate of 2,000 rpm
which is at least 60% of the coefficient of lift CL at a Reynolds
number of 80,000 and a spin rate of 2,000 rpm.
6. The multi-piece solid golf ball of claim 5 which uses at least
five types of dimples of differing diameter and/or depth, and which
includes from 6 to 30 small dimples having a diameter of 3.0 mm or
less.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of copending
application Ser. No. 12/975,018 filed on Dec. 21, 2010, the entire
contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a multi-piece solid golf
ball composed of a core, an intermediate layer and a cover that
have been formed as successive layers. More specifically, the
invention relates to a multi-piece solid golf ball which has an
improved flight performance and a good, solid feel on impact.
[0003] Numerous golf balls with a three-piece construction that
includes, as mentioned below, an intermediate layer situated
between a core and a cover, the respective layers having specific
hardnesses and thicknesses, have hitherto been disclosed as solid
golf balls which address the needs of professional golfers and
skilled amateurs. Some of these prior-art golf balls also possess
improved spin properties, flight performance and durability.
[0004] U.S. Pat. No. 6,632,149 discloses a golf ball having an
intermediate layer/cover hardness relationship which is soft/hard,
and in which the intermediate layer is thinly formed. U.S. Pat. No.
4,109,778 discloses a golf ball in which the intermediate
layer/cover hardness relationship is soft/hard, and which has an
optimized core hardness profile. U.S. Pat. No. 4,045,089 discloses
a golf ball in which the intermediate layer/cover hardness
relationship is hard/soft, and wherein the intermediate layer is
thin, having a thickness of less than 1 mm. U.S. Pat. No. 4,247,030
discloses a golf ball in which the intermediate layer/cover
hardness relationship is soft/hard, and which uses polyurethane as
the cover material. U.S. Pat. No. 2,910,516 discloses a golf ball
in which the cover has been formed so as to be relatively thicker
than the intermediate layer. U.S. Pat. No. 3,661,812 discloses a
golf ball in which the hardness difference between the core surface
and the intermediate layer is optimized, the intermediate
layer/cover hardness relationship is hard/soft, and which has a
modified dimple design. U.S. Pat. No. 3,516,125 discloses a golf
ball in which the cover is composed primarily of polyurethane, the
intermediate layer/cover hardness relationship is hard/soft, and
which has a modified dimple design. U.S. Pat. No. 3,601,582
discloses a golf ball which has a suitable core deflection under
predetermined loading, a suitable intermediate layer hardness and a
suitable cover hardness, and in which the dimple trajectory volume
has been quantitatively optimized.
[0005] However, the degree of improvement achieved in these golf
balls remains inadequate. In particular, there exists a desire for
improvements that strike a good balance between a lower spin rate,
an increased distance on shots with a W#1, and a good feel on
impact.
SUMMARY OF THE INVENTION
[0006] It is therefore an object of the present invention to
provide a multi-piece solid golf ball which is endowed with both an
excellent distance and a good, solid feel on impact.
[0007] The inventors have conducted extensive investigations in
order to attain the above object. As a result, they have discovered
that, in a multi-piece solid golf ball having an intermediate layer
situated between a core and a cover, by forming the core of a base
rubber, forming the intermediate layer and the cover each of a
resin material, setting the ratio a/b between the intermediate
layer thickness (a) and the cover thickness (b) within a given
range, setting the ratio a/c between the intermediate layer
thickness (a) and the core diameter (c) within a given range, and
optimizing the material hardness of the intermediate layer and the
material hardness of the cover, it is possible to improve the ball
rebound and improve the spin rate-lowering effect on shots with a
driver, thereby increasing the distance traveled by the ball, in
addition to which a good, solid feel can be obtained on shots with
a driver.
[0008] Accordingly, the invention provides the following
multi-piece solid golf ball. [0009] [1] A multi-piece solid golf
ball comprising a core, at least one intermediate layer encasing
the core, and a cover of at least one layer encasing the
intermediate layer, wherein the core is formed of a base rubber,
the intermediate layer and cover are each formed of a resin
material, the intermediate layer has a thickness (a) and the cover
has a thickness (b) such that the ratio a/b is from 0.7 to 1.9, the
core has a diameter (c) such that the ratio c/a with the
intermediate layer thickness (a) is from 23 to 38, the intermediate
layer has a material hardness (Shore D) of from 42 to 76, the cover
has a material hardness (Shore D) of from 41 to 69, and the ball
satisfies the following relationship: cover material
hardness<intermediate layer material hardness>core surface
hardness, and wherein a Shore D hardness at the core surface minus
a Shore D hardness at the core center is not more than 17 units.
[0010] [2] The multi-piece solid golf ball of [1] wherein, letting
the ball deflection (mm) when compressed under a final load of 490
N (50 kgf) from an initial load state of 98 N (10 kgf) be A and
letting the ball deflection (mm) when compressed under a final load
of 5,880 N (600 kgf) from an initial load state of 98 N (10 kgf) be
B, the value of B/A.times.100 is from 830 to 930. [0011] [3] The
multi-piece solid golf ball of [1], wherein the ball deflection B
is from 7.0 to 10.0 mm, and the core deflection when compressed
under a final load of 1,275 N (130 kgf) from an initial load state
of 98 N (10 kgf) is from 2.1 to 4.1 mm. [0012] [4] The multi-piece
solid golf ball of [1], wherein the resin material of the cover is
formed by injection molding a single resin blend composed primarily
of (A) a thermoplastic polyurethane and (B) a polyisocyanate
compound, which resin blend includes a polyisocyanate compound in
at least some portion of which all the isocyanate groups on the
molecule remain in an unreacted state. [0013] [5] The multi-piece
solid golf ball of [1], wherein a plurality of dimples are formed
on a surface of the ball, the total number of dimples is from 250
to 350, the dimples have a surface coverage (SR) of at least 75%,
and the ball, when hit, has a coefficient of lift CL of the ball at
a Reynolds number of 70,000 and a spin rate of 2,000 rpm which is
at least 60% of the coefficient of lift CL at a Reynolds number of
80,000 and a spin rate of 2,000 rpm. [0014] [6] The multi-piece
solid golf ball of [5] which uses at least five types of dimples of
differing diameter and/or depth, and which includes from 6 to 30
small dimples having a diameter of 3.0 mm or less.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0015] FIG. 1 is a schematic sectional view showing a multi-piece
solid golf ball (three-layer construction) according to the
invention.
[0016] FIG. 2 shows a dimple pattern used in a ball according to
one embodiment of the invention, (A) being a top view and (B) being
a side view.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The invention is described more fully below.
[0018] The multi-piece solid golf ball of the present invention, as
shown in FIG. 1, is a golf ball G having a core 1, an intermediate
layer 2 encasing the core, and a cover 3 encasing the intermediate
layer. The cover has a plurality of dimples D formed on the surface
thereof. The core 1, intermediate layer 2 and cover 3 are each not
limited to a single layer, and may be formed of a plurality of two
or more layers.
[0019] In the invention, the core has a diameter which, although
not subject to any particular limitation, is preferably at least
35.7 mm, more preferably at least 36.7 mm, and even more preferably
at least 37.7 mm. The diameter upper limit, although not subject to
any particular limitation, is preferably not more than 41.7 mm,
more preferably not more than 40.7 mm, and even more preferably not
more than 39.7 mm. At a core diameter outside this range, the ball
may have a lower initial velocity or a poor feel on impact.
[0020] The core has a center hardness which, although not subject
to any particular limitation, has a Shore hardness value of
preferably at least 35, more preferably at least 36, and even more
preferably at least 37. The upper limit, although not subject to
any particular limitation, is preferably not more than 54, more
preferably not more than 53, and even more preferably not more than
52. If this value is too small, the rebound may be inadequate, as a
result of which a sufficient distance may not be achieved. On the
other hand, if this value is too large, the spin rate of the ball
on full shots by a driver may become too high, as a result of which
a sufficient distance may not be achieved. And, the feel of the
ball may become hard.
[0021] On the other hand, the core has a surface hardness which,
although not subject to any particular limitation, has a Shore
hardness value of preferably at least 45, more preferably at least
46, and even more preferably at least 47. The upper limit, although
not subject to any particular limitation, is preferably not more
than 73, more preferably not more than 68, and even more preferably
not more than 66. If this value is too small, the rebound may be
inadequate, as a result of which a sufficient distance may not be
achieved, and the ball may have a poor durability to cracking on
repeated impact. On the other hand, if this value is too large, the
feel of the ball on full shots may become hard and the spin rate
may become too high, as a result of which a sufficient distance may
not be achieved.
[0022] In the present invention, it is critical that a Shore D
hardness at the core surface minus a Shore D hardness at the core
center is not more than 17 units. The upper limit of the above
value is preferably not more than 16 and more preferably not more
than 15. If this value is too great, the ball on full shots may
deform largely to yield an initial velocity loss of the ball, as a
result of which a sufficient distance may not be achieved.
[0023] The core has a deflection under loading, i.e., a deflection
(mm) when compressed under a final load of 1,275 N (130 kgf) from
an initial load state of 98 N (10 kgf), which, although not subject
to any particular limitation, is preferably at least 2.1 mm, more
preferably at least 2.4 mm, and even more preferably at least 2.7
mm. The upper limit, although not subject to any particular
limitation, is preferably not more than 4.1 mm, more preferably not
more than 3.8 mm, and even more preferably not more than 3.5 mm. If
this value is too large, the ball may have an inadequate rebound,
as a result of which a sufficient distance may not be achieved, and
the ball may have a poor durability to cracking under repeated
impact. On the other hand, if this value is too large, the feel on
full shots may become hard and the spin rate may become too high,
as a result of which a sufficient distance may not be achieved.
[0024] The material making up the core having the above desired
properties is not subject to any particular limitation. The core
may be formed using a rubber composition containing, for example, a
co-crosslinking agent, an organic peroxide, an inert filler and an
organosulfur compound. It is preferable to use a polybutadiene as
the base rubber of this rubber composition.
[0025] It is desirable for the polybutadiene to have a cis-1,4 bond
content on the polymer chain of at least 60 wt %, preferably at
least 80 wt %, more preferably at least 90 wt %, and most
preferably at least 95 wt %. Too low a cis-1,4 bond content among
the bonds on the molecule may result in a lower resilience.
[0026] Also, the polybutadiene has a 1,2-vinyl bond content on the
polymer chain of generally not more than 2%, preferably not more
than 1.7%, and more preferably not more than 1.5%. Too high a
1,2-vinyl bond content may result in a lower resilience.
[0027] To obtain a molded and vulcanized rubber composition which
has a high resilience and thus increases the distance traveled by
the ball, the above polybutadiene is preferably one synthesized
with a rare-earth catalyst or a Group VIII metal compound catalyst.
Polybutadiene synthesized with a rare-earth catalyst is especially
preferred.
[0028] Such rare-earth catalysts are not subject to any particular
limitation. Exemplary rare-earth catalysts include those made up of
a combination of a lanthanide series rare-earth compound with an
organoaluminum compound, an alumoxane, a halogen-bearing compound
and an optional Lewis base.
[0029] Examples of suitable lanthanide series rare-earth compounds
include halides, carboxylates, alcoholates, thioalcoholates and
amides of atomic number 57 to 71 metals.
[0030] In particular, the use of a neodymium catalyst in which a
neodymium compound serves as the lanthanide series rare-earth
compound is advantageous because it enables a polybutadiene rubber
having a high cis-1,4 bond content and a low 1,2-vinyl bond content
to be obtained at an excellent polymerization activity. Preferred
examples of such rare-earth catalysts include those mentioned in
JP-A 11-35633, JP-A 11-164912 and JP-A 2002-293996.
[0031] To increase the resilience, it is preferable for the
polybutadiene synthesized using the lanthanide series rare-earth
compound catalyst to account for at least 10 wt %, preferably at
least 20 wt %, and more preferably at least 40 wt %, of the rubber
components.
[0032] Rubber components other than the above-described
polybutadiene may be included in the base rubber insofar as the
objects of the invention are attainable. Illustrative examples of
rubber components other than the above-described polybutadiene
include other polybutadienes, and other diene rubbers, such as
styrene-butadiene rubber, natural rubber, isoprene rubber and
ethylene-propylene-diene rubber.
[0033] Examples of co-crosslinking agents include unsaturated
carboxylic acids and the metal salts of unsaturated carboxylic
acids.
[0034] Specific examples of unsaturated carboxylic acids include
acrylic acid, methacrylic acid, maleic acid and fumaric acid.
Acrylic acid and methacrylic acid are especially preferred.
[0035] The metal salts of unsaturated carboxylic acids, while not
subject to any particular limitation, are exemplified by the
above-mentioned unsaturated carboxylic acids neutralized with a
desired metal ion. Specific examples include the zinc salts and the
magnesium salts of methacrylic acid and acrylic acid. The use of
zinc acrylate is especially preferred.
[0036] The amount of unsaturated carboxylic acid and/or metal salt
thereof included per 100 parts by weight of the base rubber is set
to generally at least 10 parts by weight, preferably at least 15
parts by weight, and more preferably at least 20 parts by weight.
The upper limit is set to generally not more than 60 parts by
weight, preferably not more than 50 parts by weight, more
preferably not more than 45 parts by weight, and most preferably
not more than 40 parts by weight. Too much may make the core too
hard, giving the ball an unpleasant feel on impact, whereas too
little may lower the rebound.
[0037] The organic peroxide may be a commercially available
product, suitable examples of which include Percumyl D (available
from NOF Corporation), Perhexa 3M (NOF Corporation), and Luperco
231XL (Atochem Co.). These may be used singly or as a combination
of two or more thereof.
[0038] The amount of organic peroxide included per 100 parts by
weight of the base rubber is set to generally at least 0.1 part by
weight, preferably at least 0.3 part by weight, more preferably at
least 0.5 part by weight, and most preferably at least 0.7 part by
weight. The upper limit is set to generally not more than 5 parts
by weight, preferably not more than 4 parts by weight, more
preferably not more than 3 parts by weight, and most preferably not
more than 2 parts by weight. Too much or too little organic
peroxide may make it impossible to achieve a ball having a good
feel, durability and rebound.
[0039] Examples of preferred inert fillers include zinc oxide,
barium sulfate and calcium carbonate. These may be used singly or
as a combination of two or more thereof.
[0040] The amount of inert filler included per 100 parts by weight
of the base rubber is set to generally at least 1 part by weight,
and preferably at least 5 parts by weight. The upper limit is set
to generally not more than 50 parts by weight, preferably not more
than 40 parts by weight, more preferably not more than 30 parts by
weight, and most preferably not more than 20 parts by weight. Too
much or too little inert filler may make it impossible to achieve a
proper weight and a good rebound.
[0041] In addition, an antioxidant may be included if necessary.
Illustrative examples of suitable commercial antioxidants include
Nocrac NS-6, Nocrac NS-30 (both available from Ouchi Shinko
Chemical Industry Co., Ltd.), and Yoshinox 425 (Yoshitomi
Pharmaceutical Industries, Ltd.). These may be used singly or as a
combination of two or more thereof.
[0042] The amount of antioxidant included per 100 parts by weight
of the base rubber is preferably at least 0.05 part by weight, more
preferably at least 0.1 part by weight, and most preferably at
least 0.2 part by weight. The upper limit is generally not more
than 3 parts by weight, preferably not more than 2 parts by weight,
more preferably not more than 1 part by weight, and most preferably
not more than 0.5 part by weight. Too much or too little
antioxidant may make it impossible to achieve a good rebound and
durability.
[0043] To enhance the rebound of the golf ball and increase its
initial velocity, it is preferable to include an organosulfur
compound in the above core. Here, it is recommended that, for
example, a thiophenol, a thionaphthol, a halogenated thiophenol, or
a metal salt thereof be included as the organosulfur compound.
Specific examples include pentachlorothiophenol,
pentafluorothiophenol, pentabromothiophenol, p-chlorothiophenol,
the zinc salt of pentachlorothiophenol, and also
diphenylpolysulfides, dibenzylpolysulfides, dibenzoylpolysulfides,
dibenzothiazoylpolysulfides and dithiobenzoylpolysulfides having 2
to 4 sulfurs. The use of diphenyldisulfide or of the zinc salt of
pentachlorothiophenol is especially preferred.
[0044] The amount of organosulfur compound included per 100 parts
by weight of the base rubber is preferably at least 0.05 part by
weight, more preferably at least 0.1 part by weight, and even more
preferably at least 0.2 part by weight. If the amount included is
too small, a rebound-improving effect is unlikely to occur. The
upper limit in the amount of organosulfur compound included per 100
parts by weight of the base rubber is preferably not more than 5
parts by weight, more preferably not more than 3 parts by weight,
and even more preferably not more than 2.5 parts by weight. If the
amount included is too large, a further rebound-improving effect
(especially on shots with a W#1) is unlikely to occur, or the core
may become too soft, resulting in a poor feel.
[0045] It is desirable to produce the core by using a conventional
mixer, such as a Banbury mixer or a roll mill, to masticate the
core composition obtained by blending the above ingredients, then
compression-molding or injection-molding the composition in a
core-forming mold. The molded body obtained is then suitably heated
and cured at a temperature sufficient for the crosslinking agent
and co-crosslinking agent to act, generally from about 130.degree.
C. to about 170.degree. C., and especially from 150.degree. C. to
160.degree. C., for a period of from 10 to 40 minutes, and
especially from 12 to 20 minutes, so as to give a core having a
given hardness profile.
[0046] Next, the intermediate layer is described.
[0047] The intermediate layer has a material hardness, expressed as
the Shore D hardness (measured with a type D durometer in general
accordance with ASTM D 2240; the same applies below), which is at
least 42, preferably at least 43, and more preferably at least 44.
The upper limit is not more than 76, preferably not more than 73,
more preferably not more than 70, even more preferably 68, and most
preferably 66. If the intermediate layer is too soft, the ball may
have too much spin receptivity on full shots, as a result of which
a good distance may not be achieved. On the other hand, if the
intermediate layer is too hard, the durability of the ball to
cracking on repeated impact may worsen and the ball may have too
hard a feel when played with a putter or on short approach
shots.
[0048] The intermediate layer has a thickness which is preferably
at least 0.7 mm, more preferably at least 0.9 mm, and even more
preferably at least 1.1 mm. The upper limit is preferably not more
than 1.7 mm, more preferably not more than 1.5 mm, and even more
preferably not more than 1.3 mm. If the intermediate layer is
thicker than the above range, the spin rate-lowering effect on
shots with a W#1 may be inadequate, as a result of which a good
distance may not be achieved. On the other hand, if the
intermediate layer is too thin, the durability of the ball to
cracking on repeated impact and the low-temperature durability may
worsen.
[0049] The intermediate layer material is not subject to any
particular limitation, although use may be made of various types of
thermoplastic resins or thermoplastic elastomers. The use of a
resin composition composed primarily of an ionomer is especially
preferred. Specifically, a resin composition obtained by the
mixture of a zinc ion-neutralized ionomer with a sodium
ion-neutralized ionomer is desirable. The mixing ratio I/II between
the zinc ion-neutralized ionomer (I) and the sodium ion-neutralized
ionomer (II), expressed as a weight ratio, is preferably from 25/75
to 75/25, more preferably from 35/65 to 65/35, and even more
preferably from 45/55 to 55/45. Outside of this range, when a
zinc-neutralized ionomer and a sodium-neutralized ionomer are
mixed, the rebound of the ball as a whole may become too low, as a
result of which the desired distance may not be obtained, or the
durability to cracking under repeated impact at normal temperatures
may worsen, in addition to which the durability to cracking at low
(sub-zero Celsius) temperatures may worsen.
[0050] Also, in cases where, as is subsequently described,
polyurethane is used as the cover material, it is desirable to
abrade the surface of the intermediate layer so as to increase
adhesion with the urethane cover material. In addition, it is
desirable to apply a primer to the surface of the intermediate
layer following such abrasion treatment or to add an
adhesion-reinforcing agent to the intermediate layer material.
Ratio of Core Diameter to Intermediate Layer Thickness
[0051] In this invention, it is desirable to optimize the ratio of
the core diameter to the intermediate cover thickness within a
given range. Specifically, the ratio c/a of the core diameter (c)
to the intermediate layer thickness (a) is from 23 to 38,
preferably from 24 to 38, and more preferably from 25 to 38. If
this value is too small, the feel on impact may harden or the
rebound may be inadequate, as a result of which a sufficient
distance may not be achieved. On the other hand, if this value is
too large, the feel on impact may harden or the spin receptivity
may be excessive, as a result of which a sufficient distance may
not be achieved.
[0052] Next, the cover used in the invention has a material
hardness, expressed as the Shore D hardness, of at least 41,
preferably at least 42, and more preferably at least 43. The upper
limit is preferably not more than 69, more preferably not more than
66, and even more preferably not more than 63. If the cover is
softer than the above range, the ball may have too much spin
receptivity, as a result of which a good distance may not be
achieved on shots with a W#1. On the other hand, if the cover is
harder than the above range, the ball may lack spin receptivity on
approach shots, as a result of which the controllability may be
inadequate even for professional golfers and skilled amateurs.
[0053] The cover has a thickness which is preferably at least 0.4
mm, more preferably at least 0.6 mm, and even more preferably at
least 0.8 mm. The upper limit is not more than 1.4 mm, preferably
not more than 1.2 mm, and more preferably not more than 1.0 mm. If
the cover is thicker than the above range, the ball may have an
excessive spin receptivity on shots with a W#1, as a result of
which a good distance may not be obtained. On the other hand, if
the cover is thinner than the above range, the ball may have too
little spin receptivity in the short game, and may thus have a poor
controllability.
[0054] The cover material is not subject to any particular
limitation, although use may be made of various types of
thermoplastic resins and thermoplastic elastomers, with formation
typically being carried out using polyurethane in particular as the
primary material. From the standpoint of productivity, a
thermoplastic polyurethane elastomer is preferred.
[0055] Specifically, it is preferable to use a specific
thermoplastic polyurethane composition composed primarily of (A) a
thermoplastic polyurethane and (B) a polyisocyanate compound. This
resin blend is described below.
[0056] To fully and effectively achieve the objects of the
invention, a necessary and sufficient amount of unreacted
isocyanate groups should be present within the cover resin
material. Specifically, it is recommended that the total weight of
components A and B combined be preferably at least 60%, and more
preferably at least 70%, of the overall weight of the cover layer.
Above components A and B are described in detail below.
[0057] In describing the thermoplastic polyurethane (A), the
structure of this thermoplastic polyurethane includes soft segments
composed of a polymeric polyol that is a long-chain polyol
(polymeric glycol), and hard segments composed of a chain extender
and a polyisocyanate compound. Here, the long-chain polyol used as
a starting material is not subject to any particular limitation,
and may be any that is used in the prior art relating to
thermoplastic polyurethanes. Exemplary long-chain polyols include
polyester polyols, polyether polyols, polycarbonate polyols,
polyester polycarbonate polyols, polyolefin polyols, conjugated
diene polymer-based polyols, castor oil-based polyols,
silicone-based polyols and vinyl polymer-based polyols. These
long-chain polyols may be used singly or as combinations of two or
more thereof. Of the long-chain polyols mentioned here, polyether
polyols are preferred because they enable the synthesis of
thermoplastic polyurethanes having a high rebound resilience and
excellent low-temperature properties.
[0058] Illustrative examples of the above polyether polyol include
poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene
glycol) and poly(methyltetramethylene glycol) obtained by the
ring-opening polymerization of cyclic ethers. The polyether polyol
may be used singly or as a combination of two or more thereof. Of
the above, poly(tetramethylene glycol) and/or
poly(methyltetramethylene glycol) are preferred.
[0059] It is preferable for these long-chain polyols to have a
number-average molecular weight in a range of 1,500 to 5,000. By
using a long-chain polyol having a number-average molecular weight
within this range, golf balls made with a thermoplastic
polyurethane composition having excellent properties such as
resilience and manufacturability can be reliably obtained. The
number-average molecular weight of the long-chain polyol is more
preferably in a range of 1,700 to 4,000, and even more preferably
in a range of 1,900 to 3,000.
[0060] The number-average molecular weight of the long-chain polyol
refers here to the number-average molecular weight computed based
on the hydroxyl number measured in accordance with JIS K-1557.
[0061] Chain extenders that may be suitably used include those
employed in the prior art relating to thermoplastic polyurethanes.
For example, low-molecular-weight compounds which have a molecular
weight of 400 or less and bear on the molecule two or more active
hydrogen atoms capable of reacting with isocyanate groups are
preferred. Illustrative, non-limiting, examples of the chain
extender include 1,4-butylene glycol, 1,2-ethylene glycol,
1,3-butanediol, 1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. Of
these chain extenders, aliphatic diols having 2 to 12 carbons are
preferred, and 1,4-butylene glycol is more preferred.
[0062] The polyisocyanate compound is not subject to any particular
limitation; preferred use may be made of one that is used in the
prior art relating to thermoplastic polyurethanes. Specific
examples include one or more selected from the group consisting of
4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate,
2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene
diisocyanate, naphthylene-1,5-diisocyanate, tetramethylxylene
diisocyanate, hydrogenated xylylene diisocyanate,
dicyclohexylmethane diisocyanate, tetramethylene diisocyanate,
hexamethylene diisocyanate, isophorone diisocyanate, norbornene
diisocyanate, trimethylhexamethylene diisocyanate and dimer acid
diisocyanate. Depending on the type of isocyanate used, the
crosslinking reaction during injection molding may be difficult to
control. In the practice of the invention, to provide a balance
between stability at the time of production and the properties that
are manifested, it is most preferable to use 4,4'-diphenylmethane
diisocyanate, which is an aromatic diisocyanate.
[0063] It is most preferable for the thermoplastic polyurethane
serving as above component A to be a thermoplastic polyurethane
synthesized using a polyether polyol as the long-chain polyol,
using an aliphatic diol as the chain extender, and using an
aromatic diisocyanate as the polyisocyanate compound. It is
desirable, though not essential, for the polyether polyol to be a
polytetramethylene glycol having a number-average molecular weight
of at least 1,900, for the chain extender to be 1,4-butylene
glycol, and for the aromatic diisocyanate to be
4,4'-diphenylmethane diisocyanate.
[0064] The mixing ratio of active hydrogen atoms to isocyanate
groups in the above polyurethane-forming reaction may be adjusted
within a desirable range so as to make it possible to obtain a golf
ball which is composed of a thermoplastic polyurethane composition
and has various improved properties, such as rebound, spin
performance, scuff resistance and manufacturability. Specifically,
in preparing a thermoplastic polyurethane by reacting the above
long-chain polyol, polyisocyanate compound and chain extender, it
is desirable to use the respective components in proportions such
that the amount of isocyanate groups on the polyisocyanate compound
per mole of active hydrogen atoms on the long-chain polyol and the
chain extender is from 0.95 to 1.05 moles.
[0065] No particular limitation is imposed on the method of
preparing the thermoplastic polyurethane used as component A.
Production may be carried out by either a prepolymer process or a
one-shot process which uses a long-chain polyol, a chain extender
and a polyisocyanate compound and employs a known urethane-forming
reaction. Of these, a process in which melt polymerization is
carried out in a substantially solvent-free state is preferred.
Production by continuous melt polymerization using a multiple screw
extruder is especially preferred.
[0066] It is also possible to use a commercially available product
as the thermoplastic polyurethane serving as component A.
Illustrative examples include Pandex T8295, Pandex T8290 and Pandex
T8260 (all available from DIC Bayer Polymer, Ltd.).
[0067] Next, concerning the polyisocyanate compound used as
component B, it is necessary that, in a single resin blend (in the
form of pellets) prior to molding, all the isocyanate groups in at
least some portion of the polyisocyanate compound remain in an
unreacted state. That is, some polyisocyanate compound in which the
isocyanate groups on the molecule remain in a completely free state
must be present in the resin blend; such a polyisocyanate compound
may be present together with polyisocyanate compound in which only
one end of the molecule is in a free state.
[0068] Various types of isocyanates may be employed without
particular limitation as the polyisocyanate compound. Illustrative
examples include one or more selected from the group consisting of
4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate,
2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene
diisocyanate, naphthylene-1,5-diisocyanate, tetramethylxylene
diisocyanate, hydrogenated xylylene diisocyanate,
dicyclohexylmethane diisocyanate, tetramethylene diisocyanate,
hexamethylene diisocyanate, isophorone diisocyanate, norbornene
diisocyanate, trimethylhexamethylene diisocyanate and dimer acid
diisocyanate. Of the above group of isocyanates, the use of
4,4'-diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate
and isophorone diisocyanate is preferable in terms of the balance
between the influence on processability of, e.g., the rise in
viscosity accompanying the reaction with the thermoplastic
polyurethane serving as component A and the physical properties of
the resulting golf ball cover material.
[0069] In the invention, although not an essential constituent, a
thermoplastic elastomer other than the above-described
thermoplastic polyurethane may be included as component C together
with components A and B. Including this component C in the above
resin blend enables the flow properties of the resin blend to be
further improved and enables improvements to be made in various
properties required of golf ball cover materials, such as
resilience and scuff resistance.
[0070] In addition to the above resin components, various additives
may be optionally included in the above-described cover-forming
resin material. Examples of such additives include pigments,
dispersants, antioxidants, ultraviolet absorbers, ultraviolet
stabilizers, parting agents, plasticizers and inorganic fillers
(e.g., zinc oxide, barium sulfate, titanium dioxide).
Ratio of Intermediate Layer Thickness to Cover Thickness
[0071] In the invention, it is desirable to optimize the ratio of
the intermediate layer thickness to the cover thickness within a
given range. Specifically, the ratio a/b of the intermediate layer
thickness (a) to the cover thickness (b) is from 0.7 to 1.9,
preferably from 0.8 to 1.9, and more preferably from 0.9 to 1.9. If
this value is too small, the feel on impact may harden or the spin
receptivity may be excessive, as a result of which a sufficient
distance may not be achieved. On the other hand, if this value is
too large, the rebound may be inadequate, as a result of which a
sufficient distance may not be achieved.
Relationship Between Intermediate Layer Material Hardness, Cover
Material Hardness and Core Surface Hardness
[0072] An essential condition in the invention is that the
intermediate layer material hardness, the cover material hardness
and the core surface hardness satisfy the following relationship
therebetween:
cover material hardness<intermediate layer material
hardness>core surface hardness.
By setting the hardnesses of the respective layers so as to
maintain this relationship, it is possible to further enhance the
flight performance and to obtain a good, solid feel on impact.
[0073] In the invention, a plurality of dimples are formed on the
surface of the cover. The number of dimples arranged on the cover
surface, although not subject to any particular limitation, is
preferably at least 250, more preferably at least 300, and even
more preferably at least 318. The upper limit is preferably not
more than 350, and more preferably not more than 328. If the number
of dimples is larger than the above range, the ball trajectory may
become lower, possibly decreasing the distance traveled by the
ball. On the other hand, if the number of dimples is smaller than
the above range, the ball trajectory may become higher, as a result
of which an increased distance may not be achieved.
[0074] The shapes of the dimples are not subject to any particular
limitation; any one type, or combination of two or more types, from
among, e.g., circular shapes, various polygonal shapes, dewdrop
shapes and oval shapes may be suitably selected. For example, in
cases where circular dimples are used, dimples having a diameter of
from 2.5 to 6.0 mm may be suitably selected. As for the number of
dimple types, by suitably using from at least 3 to 5 or more types,
and preferably 5 or more types, it is possible to cover the
spherical surface with dimples in a manner that is uniform and
well-balanced.
[0075] The types of dimples are not subject to any particular
limitation. The dimples may be suitably arranged in a spherical
polyhedral configuration that is based on a repeated pattern of
unit polygons, such as unit triangles and unit pentagons. Moreover,
it is possible to use all the dimples at slightly varying
diameters. In such a case, the number of dimple types may be set to
20 or more. To fully manifest the aerodynamic properties, it is
desirable for the sum of the dimple surface areas, each defined by
the border of the flat plane circumscribed by the edge of a dimple,
when expressed as a ratio with respect to the spherical surface of
the ball were it to be free of dimples, to be at least 75%.
[0076] In addition, it is preferable for the ball to include at
least six small dimples having a diameter of 3.0 mm or less, with
the number of such dimples being more preferably in a range of from
6 to 30. In the invention, by intermingling large and small dimples
so as to increase the surface coverage, it is possible to achieve
the effect of, in the first half of the ball trajectory, making the
coefficient of lift (CL) larger and making the coefficient of drag
(CD) smaller. Making the drag or the coefficient of drag CD smaller
is not by itself very effective for increasing the distance
traveled on a shot. Simply reducing the coefficient of drag does
extend the position of the highest point on the trajectory, but
tends to result in a loss in carry because the ball drops on
account of insufficient lift in the low-velocity portion of the
trajectory after the highest point. Accordingly, in the multi-piece
solid golf ball of the invention, it is preferable for the ball to
have a coefficient of drag CD of 0.225 or below when the Reynolds
number is 180,000 and the spin rate is 2,520 rpm immediately after
being hit and launched, and for the ball, when hit, to have a
coefficient of lift CL at a Reynolds number of 70,000 and a spin
rate of 2000 rpm which remains at least 60% of the coefficient of
lift CL at a Reynolds number of 80,000 and a spin rate of 2,000
rpm. A Reynolds number of 180,000 immediately after the ball is hit
and launched corresponds to a ball velocity of about 66 m/s, and
Reynolds numbers of 80,000 and 70,000 correspond to velocities of
about 30 m/s and 26 m/s, respectively.
[0077] The golf ball of the invention can be manufactured so as to
conform with the Rules of Golf for competitive play, with the ball
preferably being of a diameter that will not pass through a ring
having an inside diameter of 42.672 mm, but is not more than 42.80
mm, and of a weight that is generally from 45.0 to 45.93 g.
Ball Deflection
[0078] In the present invention, letting the ball deflection (mm)
when compressed under a final load of 490 N (50 kgf) from an
initial load state of 98 N (10 kgf) be A and letting the ball
deflection (mm) when compressed under a final load of 5,880 N (600
kgf) from an initial load state of 98 N (10 kgf) be B, the value of
B/A.times.100 is from 830 to 930, preferably from 840 to 920, and
more preferably from 830 to 910. If the above value is too small,
the ball may have too much spin receptivity on shots with a driver,
as a result of which a sufficient distance may not be achieved. On
the other hand, if the above value is too large, the initial
velocity on shots with a driver may be inadequate, as a result of
which a sufficient distance may not be achieved.
[0079] The ball deflection B, although not subject to any
particular limitation, is preferably from 7.0 to 10.0 mm.
[0080] The ball has a deflection (mm), when compressed under a
final load of 1,275 N (130 kgf) from an initial load state of 98 N
(10 kgf), which, although not subject to any particular limitation,
is preferably at least 2.1 mm, more preferably at least 2.2 mm, and
even more preferably at least 2.3 mm. The upper limit, although not
subject to any particular limitation, is preferably not more than
2.9 mm, more preferably not more than 2.8 mm, and even more
preferably not more than 2.7 mm.
[0081] As described above, the multi-piece solid golf ball of the
invention has an improved flight performance and a good, solid feel
on impact.
EXAMPLES
[0082] Examples of the invention and Comparative Examples are given
below by way of illustration, and not by way of limitation.
Examples 1 to 3, Comparative Examples 1 to 3
[0083] Rubber compositions were formulated as shown in Table 1
below, then molded and vulcanized at 155.degree. C. for 13 minutes
to form solid cores.
TABLE-US-00001 TABLE 1 Example Comparative Example (parts by
weight) 1 2 3 1 2 3 Polybutadiene A 80 80 80 80 80 80 Polybutadiene
B 20 20 20 20 20 20 Peroxide 1.2 1.2 1.2 1.2 1.2 1.2 Barium sulfate
13.3 14.6 16.1 22.0 13.8 14.0 Zinc oxide 4.0 4.0 4.0 4.0 4.0 4.0
Antioxidant 0.1 0.1 0.1 0.1 0.1 0.1 Zinc acrylate 31.7 30.5 29.3
25.9 34.5 33.5 Zinc stearate -- -- -- -- -- 5 Sulfur -- -- -- -- --
0.12 Zinc salt of 0.2 0.2 0.2 0.2 0.2 0.2 pentachlorothiophenol
[0084] Details on the above core materials are given below. Numbers
in the table represent parts by weight. [0085] Polybutadiene A:
Available under the trade name "BR 730" from JSR Corporation.
[0086] Polybutadiene B: Available under the trade name "BR 01" from
JSR Corporation. [0087] Peroxide: A mixture of
1,1-di(t-butylperoxy)cyclohexane and silica, available under the
trade name "Perhexa C-40" from NOF Corporation. [0088] Antioxidant:
2,2'-Methylenebis(4-methyl-6-t-butylphenol), available under the
trade name "Nocrac NS-6" from Ouchi Shinko Chemical Industry Co.,
Ltd. [0089] Barium sulfate: Available under the trade name
"Precipitated Barium #300" from Sakai Chemical Co., Ltd.
Formation of Intermediate Layer and Cover
[0090] Next, using the No. 1, No. 2 or No. 4 formulation shown in
Table 2, an intermediate layer (one or two layers) was
injection-molded over the core obtained above, thereby producing an
intermediate sphere.
[0091] Next, the respective starting material (units: parts by
weight) of No. 3 shown in Table 2 were mixed under a nitrogen
atmosphere in a twin-screw extruder, thereby giving a cover-forming
resin blend. This resin blend was in the form of pellets having a
length of 3 mm and a diameter of 1 to 2 mm.
[0092] The intermediate sphere was placed within an injection mold
and the cover material was injection-molded over this sphere,
thereby giving multi-piece solid golf balls in Examples 1 to 3 and
Comparative Examples 1 to 3. To measure the cover properties, the
cover material was injection-molded as a 2 mm thick sheet, which
was annealed at 100.degree. C. for 8 hours, then held at room
temperature for one week and subsequently furnished for
testing.
[0093] The dimples shown in FIG. 2 were formed at this time on the
cover surface in the respective examples and comparative examples.
Details on the dimples are shown in Table 3.
TABLE-US-00002 TABLE 2 (parts by weight) No. 1 No. 2 No. 3 No. 4
Himilan 1605 50 Himilan 1557 15 Himilan 1706 35 Surlyn 8120 75
Dynaron 6100P 25 AN4319 20 AN4221C 80 Magnesium stearate 60
Magnesium oxide 1.7 Behenic acid 20 Calcium hydroxide 2.3 Calcium
stearate 0.15 Zinc stearate 0.15 Trimethylolpropane 1.1 Polytail H
2 T-8295 T-8290 75 T-8293 25 Titanium oxide 3.5 Polyethylene 1
Isocyanate compound 7.5
[0094] The above trade names are explained below.
[0095] Trade names for the chief materials shown in the table are
as follows. [0096] Himilan: Ionomers available from DuPont-Mitsui
Polychemicals Co., Ltd. [0097] Surlyn: An ionomer available from
E.I. DuPont de Nemours & Co. [0098] Dynaron E6100P: A
hydrogenated polymer available from JSR Corporation. [0099] AN4319,
AN4221C: "Nucrel," available from DuPont-Mitsui Polychemicals Co.,
Ltd. [0100] Magnesium stearate: Available under the trade name
"Magnesium Stearate G" from NOF Corporation. [0101] Magnesium
oxide: "Kyowamag MF150," available from Kyowa Chemical Industry
Co., Ltd. [0102] Behenic acid: NAA222-S (beads), available from NOF
Corporation. [0103] Calcium hydroxide: CLS-B, available from
Shiraishi Kogyo. [0104] T-8925, T-8290, T-8283: MDI-PTMG type
thermoplastic polyurethanes available under the trade name "Pandex"
from DIC Bayer Polymer. [0105] Polyethylene wax: Available under
the trade name "Sanwax 161P" from Sanyo Chemical Industries, Ltd.
[0106] Isocyanate compound: 4,4'-Diphenylmethane diisocyanate
TABLE-US-00003 [0106] TABLE 3 No. Number of dimples Diameter (mm) 1
18 4.7 2 258 4.5 3 18 3.7 4 26 3.4 5 6 2.9 Dimple types 5 types
Number of dimples 326 SR (%) 80 Low-velocity CL ratio (%) 82
Dimple Definitions
[0107] Diameter: Diameter of flat plane circumscribed by edge of
dimple. [0108] Depth: Maximum depth of dimple from flat plane
circumscribed by edge of dimple. [0109] V.sub.o: Spatial volume of
dimple below flat plane circumscribed by dimple edge, divided by
volume of cylinder whose base is the flat plane and whose height is
the maximum depth of dimple from the base. [0110] SR: Sum of
individual dimple surface areas, each defined by the flat plane
circumscribed by the edge of a dimple, as a percentage of surface
area of ball sphere were it to have no dimples thereon. (units:
%)
Aerodynamic Properties (Low-Velocity CL Ratio, High-Velocity CD
Value)
[0111] The low-velocity CL ratio was obtained by calculating the
ratio of the coefficient of lift CL of a ball on its trajectory
just after launch using an Ultra Ball Launcher (UBL) at a Reynolds
number of 70,000 and a spin rate of 2,000 rpm with respect to the
coefficient of lift CL of a ball launched at a Reynolds number of
80,000 and a spin rate of 2,000 rpm. Similarly, the high-velocity
CD value was obtained by calculating the coefficient of drag when
the ball was launched at a Reynolds number or 180,000 and a spin
rate of 2,520 rpm.
[0112] The UBL is a device which includes two pairs of drums, one
on top and one on the bottom. The drums are turned by belts that
extend across the two top drums and across the two bottom drums.
The UBL inserts a golf ball between the turning drums and thereby
launches the golf ball under the desired conditions. This device is
manufactured by Automated Design Corporation.
[0113] The various golf balls obtained were tested and evaluated by
the methods described below with regard to properties of the
various layers, such as thickness, hardness and deflection, and
also flight performance and feel. The results are shown in Tables 4
and 5. All measurements were carried out in a 23.degree. C.
atmosphere.
(1) Deflection (mm) of Core and Intermediate Layer-Covered
Sphere
[0114] The core or the intermediate layer-covered sphere was
compressed at a temperature of 23.+-.1.degree. C. and a speed of 50
mm/min, and the amount of deflection (mm) incurred by the core or
sphere when subjected to a final load of 1,275 N (130 kgf) from an
initial load state of 98 N (10 kgf) was measured. The average for
10 specimens was determined.
(2) Core Surface Hardness
[0115] The durometer indenter was set substantially perpendicular
to the spherical surface of the core and the Shore D hardness (the
hardness based on a type D durometer in accordance with ASTM-2240)
was determined. The average of the two measurements was used as the
core surface hardness.
(3) Material Hardnesses of Intermediate Layer and Cover (Hardness
of Sheet-Type Molding)
[0116] The respective layer-forming materials were molded into
sheets having a thickness of about 2 mm and held for two weeks at
23.degree. C., following which the hardnesses were measured with a
type D durometer (i.e., "Shore D hardness") in accordance with
ASTM-2240.
(4) Ball Deflection (Deflection Under 50 kgf Loading, 130 kgf
Loading, and 600 kgf Loading)
[0117] The ball was compressed at a temperature of 23.+-.1.degree.
C. and a speed of 500 mm/min, and the amount of deflection (mm)
incurred by the ball when subjected to a final load of 5,880 N (600
kgf) from an initial load state of 98 N (10 kgf) was measured. The
average for 10 specimens was determined.
[0118] Also, the ball was compressed at a temperature of
23.+-.1.degree. C. and a speed of 500 mm/min, and the amount of
deflection (mm) incurred by the ball when subjected to a final load
of 490 N (50 kgf) from an initial load state of 98 N (10 kgf) was
measured. The average for 10 specimens was determined.
(5) Flight Performance on Shots with Driver
[0119] The distance traveled by the ball when hit at a head speed
(HS) of 50 m/s with a driver (abbreviated below as "W#1"; TourStage
GR (2010 model), manufactured by Bridgestone Sports Co., Ltd.; loft
angle,)10.5.degree.) mounted on a golf swing robot was measured.
The results were rated according to the criteria shown below. The
spin rate was the value measured for the ball, using an apparatus
for measuring initial conditions, immediately after the ball was
hit in the same way as described above.
[0120] Good: Carry was 245 m or more
[0121] NG: Carry was less than 245 m
(6) Feel
[0122] Golfers who value distance and have a head speed (HS) of 48
m/s hit the ball with a driver (W#1) and carried out sensory
evaluations according to the criteria shown below.
[0123] The driver (W#1) used was the same as in (5) above: a
TourStage GR (2010 model), manufactured by Bridgestone Sports Co.,
Ltd., and having a loft angle of 10.5.degree..
[0124] Good: At least seven out of ten golfers thought the ball had
a good feel.
[0125] NG: Three or fewer out of ten golfers thought the ball had a
good feel.
(A "good feel" refers to a solid feel on impact which leaves the
impression that the ball will fly far. A feel that is too soft or
too hard is regarded as a "poor feel.")
TABLE-US-00004 TABLE 4 Example Comparative Example 1 2 3 1 2 3
Dimples Total number 326 326 326 326 326 326 Low-velocity CL ratio
(%) 82 82 82 82 82 82 SR value (%) 80 80 80 80 80 80 Ball Diameter
(mm) 42.7 42.7 42.7 42.7 42.7 42.7 Deflection 1.0 1.0 1.0 0.9 1.0
1.0 under 50 kg loading (A) Deflection 2.5 2.5 2.5 2.6 2.4 2.5
under 130 kg loading Deflection 8.3 8.5 8.7 8.8 8.1 8.5 under 600
kg loading (B) Cover Material (type) No. 3 No. 3 No. 3 No. 3 No. 3
No. 3 Shore D hardness 56.5 56.5 56.5 56.5 56.5 56.5 Thickness (mm)
(b) 0.8 0.8 0.8 0.8 0.3 0.8 Intermediate Material (type) No. 1 No.
1 No. 1 No. 1 No. 1 No. 1 layer Shore D hardness 62 62 62 62 62 62
(1) Thickness (mm) (a) 1.1 1.2 1.4 1.2 1.1 1.2 Diameter of
intermediate 41.1 41.1 41.1 41.1 42.1 41.1 layer-covered sphere
(mm) Deflection 2.8 2.8 2.8 2.8 2.45 2.8 under 130 kg loading (mm)
Intermediate Material (type) No. 4 layer Shore D hardness 55 (2)
Thickness (mm) (a) 1.1 Diameter of intermediate 38.8 layer-covered
sphere (mm) Deflection 3.2 under 130 kg loading (mm) Core Diameter
(mm) (c) 39.0 38.7 38.4 36.7 40 38.7 Deflection 2.95 3.10 3.25 3.56
2.70 3.10 under 130 kg loading (mm) Shore D hardness 58 57 56 53 60
59 at surface (1) Shore D hardness 46 44 43 40 48 41 at center (2)
(1) - (2) 12 13 13 13 12 18 Ratio of intermediate layer 1.3 1.5 1.7
2.9 3.5 1.5 thickness to cover thickness (a/b) Ratio of core
diameter to 37.1 32.3 28.4 15.9 38.1 32.3 intermediate layer
thickness (c/a) Deflection ratio: 600 kg 860 886 899 937 838 886
loading to 50 kg loading (B/A .times. 100)
TABLE-US-00005 TABLE 5 Example Comparative Example 1 2 3 1 2 3
Flight Initial velocity (m/s) 72.3 72.0 71.7 71.4 72.1 71.0 (W#1)
Spin rate (rpm) 2,500 2,416 2,350 2,461 2,684 2,380 Carry (m) 246
247 245 242 244 241 Rating good good good NG NG NG Feel (W#1) good
good good NG NG NG
[0126] The results in Table 5 show that the respective comparative
examples were inferior to the present invention (working examples)
in the following ways.
[0127] In Comparative Example 1, the ratio of the core diameter to
the intermediate layer thickness was small and the initial velocity
on a shot with a W#1 was insufficient, as a result of which a good
carry was not achieved. In addition, the feel of the ball when hit
with a W#1 was too soft and left something to be desired.
[0128] In Comparative Example 2, the ratio of the core diameter to
the intermediate layer thickness was large and the spin
rate-lowering effect on shots with a W#1 was inadequate, as a
result of which a good carry was not achieved. Moreover, the feel
of the ball when hit with a W#1 was too hard.
[0129] In Comparative Example 3, a Shore D hardness at the core
surface minus a Shore D hardness at the core center is too great,
the ball on full shots deformed largely to yield an initial
velocity loss of the ball, as a result of which a good carry was
not achieved. Also, the ball on full shots deformed largely, a
result of which a sufficient good feel was not obtained and the
feel was not endowed with an expectation of good flight
distance.
* * * * *