U.S. patent application number 10/817875 was filed with the patent office on 2004-10-07 for multi-piece solid golf ball.
Invention is credited to Sasaki, Takashi.
Application Number | 20040198534 10/817875 |
Document ID | / |
Family ID | 33095314 |
Filed Date | 2004-10-07 |
United States Patent
Application |
20040198534 |
Kind Code |
A1 |
Sasaki, Takashi |
October 7, 2004 |
Multi-piece solid golf ball
Abstract
The present invention provides a multi-piece solid golf ball
having good shot feel, excellent flight performance and excellent
controllability. The present invention relates to a multi-piece
solid golf ball comprising a core composed of a center and at least
one intermediate layer formed on the center, and a cover covering
the core, wherein assuming that a central point hardness of the
center, a surface hardness of the center, a hardness of the
intermediate layer and a hardness of the cover in Shore D hardness
are represented by H.sub.M, H.sub.S, H.sub.I and H.sub.C,
respectively, the H.sub.M, H.sub.S, H.sub.I and H.sub.C satisfy a
correlation represented by the following formula:
H.sub.M<H.sub.S<H.sub.I<H.sub.C and the cover is formed
from polyurethane material as a main component, and has a hardness
in Shore D hardness of 45 to 60.
Inventors: |
Sasaki, Takashi; (Kobe-shi,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
33095314 |
Appl. No.: |
10/817875 |
Filed: |
April 6, 2004 |
Current U.S.
Class: |
473/370 ;
473/378 |
Current CPC
Class: |
A63B 37/0031 20130101;
A63B 37/0075 20130101; A63B 37/0043 20130101; A63B 37/0076
20130101; A63B 37/04 20130101; A63B 37/00621 20200801; A63B 37/0003
20130101; A63B 37/00622 20200801 |
Class at
Publication: |
473/370 ;
473/378 |
International
Class: |
A63B 037/12 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 7, 2003 |
JP |
2003-103005 |
Claims
What is claimed is:
1. A multi-piece solid golf ball comprising a core composed of a
center and at least one intermediate layer formed on the center,
and a cover covering the core, wherein assuming that a central
point hardness of the center, a surface hardness of the center, a
hardness of the intermediate layer and a hardness of the cover in
Shore D hardness are represented by H.sub.M, H.sub.S, H.sub.I and
H.sub.C, respectively, the H.sub.M, H.sub.S, H.sub.I and H.sub.C
satisfy a correlation represented by the following
formula:H.sub.M<H.sub.S<H.sub.I<H.sub.Cand the cover is
formed from polyurethane material as a main component, and has a
hardness in Shore D hardness of 45 to 60.
2. The multi-piece solid golf ball according to claim 1, wherein
the golf ball has a deformation amount of 3.0 to 4.0 mm, when
applying from an initial load of 98 N to a final load of 1274
N.
3. The multi-piece solid golf ball according to claim 1, wherein
the polyurethane material comprises polyurethane-based
thermoplastic elastomer as a main component.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a multi-piece solid golf
ball. More particularly, it relates to a multi-piece solid golf
ball having good shot feel, excellent flight performance and
excellent controllability.
BACKGROUND OF THE INVENTION
[0002] In golf balls commercially selling, there are solid golf
balls such as two-piece golf ball, three-piece golf ball and the
like, and thread wound golf balls. Recently, the two-piece golf
ball and three-piece golf ball, of which flight distance can be
improved while maintaining soft and good shot feel at the time of
hitting as good as the conventional thread wound golf ball,
generally occupy the greater part of the golf ball market.
Multi-piece solid golf balls represented by three-piece golf ball
have good shot feel while maintaining excellent flight performance,
because they can vary hardness distribution and design of golf
balls, when compared with the two-piece golf ball.
[0003] The three-piece solid golf balls are obtained by inserting
an intermediate layer between the core and the cover layer
constituting the two-piece solid golf ball and have been described
in Japanese Patent Kokai Publication Nos. 313643/1997, 305114/1998,
151226/1998, 360740/2002 and the like. In the golf balls, it has
been attempted to compromise the balance of flight performance and
shot feel at the time of hitting by using thermoplastic resin, such
as polyurethane-based thermoplastic elastomer, ionomer resin, or
mixtures thereof, for the intermediate layer, to adjust a hardness,
hardness distribution, deformation amount, specific gravity,
elastic modulus and the like of the core, intermediate layer and
cover to proper ranges.
[0004] In Japanese Patent Kokai Publication No. 313643/1997, a
three-piece solid golf ball, of which an intermediate layer is
placed between a core and a cover, is disclosed. The core has a
center hardness in JIS-C hardness of not more than 75 and has a
surface hardness in JIS-C hardness of not more than 85, the surface
hardness is higher than the center hardness by 5 to 25, a hardness
of the intermediate layer is higher than the surface hardness of
the core by less than 10, and a hardness of the cover is higher
than the hardness of the intermediate layer. In the golf ball,
since the cover is formed from ionomer resin as a base resin, the
spin performance of the resulting golf ball is not sufficiently
obtained, and the controllability is poor. In addition, the scuff
resistance is not sufficiently obtained.
[0005] In Japanese Patent Kokai Publication No. 305114/1998, a golf
ball comprising a solid core, an intermediate layer and a cover, of
which the surface of the cover has many dimples, is disclosed. The
core has a surface hardness in Shore D hardness of not more than
48, the intermediate layer has a hardness in Shore D hardness of 53
to 60 and the hardness of the intermediate layer is higher than the
surface hardness of the core by not less than 8, the cover has a
hardness in Shore D hardness of 55 to 65 and the hardness of the
cover is higher than that of the intermediate layer, the dimples
are consisted of two types having different diameter and/or depth
from each other, the total number of the dimples is within the
range of 370 to 450, the dimples cover at least 63% of the ball
surface, and the index D.sub.st of the overall dimple surface area
is at least 4. In the golf ball, since the cover is formed from
ionomer resin as a base resin, the hardness of the cover is high,
and the shot feel and controllability are poor.
[0006] In Japanese Patent Publication No. 151226/1998, a
multi-piece golf ball, of which the center has a distortion of at
least 2.5 mm under a load of 100 kg, the hardness in Shore D
hardness of the intermediate layer is at least 13 degrees higher
than that of the cover, and the ball as a whole has an inertia
moment of at least 83 g-cm.sup.2, is described. However, since the
cover has low hardness and large thickness, the rebound
characteristics of the resulting golf ball are poor and the spin
amount is large, and the flight distance when hit by a driver is
not sufficiently obtained.
[0007] In Japanese Patent Publication No. 360740/2002, a
three-piece solid golf ball comprising a core composed of a center
and an intermediate layer formed on the center, and a cover formed
on the intermediate layer, of which the cover is formed from a
mixture of polyurethane-based thermoplastic elastomer and
polyamide-based thermoplastic elastomer as a base resin, is
disclosed. Sine the cover has low hardness, the spin amount of the
resulting golf ball is large, and the flight distance when hit by a
driver is not sufficiently obtained.
[0008] In the conventional golf balls, sufficient performances have
not been obtained in view of the balance of the flight performance
and shot feel, and durability at a level of practical use, as
described above. Therefore, a golf ball, of which the shot feel,
flight performance, and durability are further improved, has been
required.
OBJECTS OF THE INVENTION
[0009] A main object of the present invention is to provide a
multi-piece solid golf ball having good shot feel, excellent flight
performance and excellent controllability.
[0010] According to the present invention, the object described
above has been accomplished by providing a multi-piece solid golf
ball, of which an intermediate layer is placed between a center and
a cover, by forming the cover from polyurethane material, and by
adjusting a hardness distribution of the central point and surface
of the center, the intermediate layer and the cover, and a hardness
of the cover to specified ranges, thereby providing a multi-piece
solid golf ball having good shot feel, excellent flight performance
and excellent controllability.
[0011] This object as well as other objects and advantages of the
present invention will become apparent to those skilled in the art
from the following description with reference to the accompanying
drawings.
BRIEF EXPLANATION OF DRAWINGS
[0012] The present invention will become more fully understood from
the detailed description given hereinbelow and the accomplishing
drawings which are given by way of illustrating only, and thus are
not limitative of the present invention, and wherein:
[0013] FIG. 1 is a schematic cross section illustrating one
embodiment of the golf ball of the present invention.
SUMMARY OF THE INVENTION
[0014] The present invention provides a multi-piece solid golf ball
comprising a center, at least one intermediate layer formed on the
center and a cover covering the intermediate layer, wherein
[0015] assuming that a central point hardness of the center, a
surface hardness of the center, a hardness of the intermediate
layer and a hardness of the cover in Shore D hardness are
represented by H.sub.M, H.sub.S, H.sub.I and H.sub.C, respectively,
the H.sub.M, H.sub.S, H.sub.I and H.sub.C satisfy a correlation
represented by the following formula:
H.sub.M<H.sub.S<H.sub.I<H.sub.C
[0016] and
[0017] the cover is formed from polyurethane material as a main
component, and has a hardness in Shore D hardness of 45 to 60.
[0018] Generally, urethane cover has been widely used for golf
balls, because the urethane material imparts the resulting golf
ball to excellent controllability. Particularly, soft urethane
cover has been widely used in order to improve the controllability.
However, since the soft urethane cover had poor rebound
characteristics, it was required to use an intermediate layer
having high stiffness (Japanese Patent Publication No.
151226/1998). Therefore, it was problem that the resulting golf
ball had also large spin amount when hit by a driver, and hit golf
ball created blown-up trajectory, which reduced the flight
distance.
[0019] Moreover, golf balls satisfying the above correlation
represented by the following formula:
(Central point hardness of the core)<(Surface hardness of the
core)<(Intermediate layer hardness)<(Cover hardness)
[0020] have been proposed (Japanese Patent Kokai Publication Nos.
313643/1997 and 305114/1998), but it was required to use a cover
comprising ionomer resin as a main component in order to have high
stiffness cover. Therefore, it was problem that the cover hardness
was too high or the spin amount at approach shot of the resulting
golf ball was small, and the controllability was not sufficiently
obtained.
[0021] In the conventional golf balls, since the soft urethane
cover has been used as an urethane cover, there has no golf ball
using urethane cover and satisfying the correlation represented by
the above formula. In the golf ball of the present invention, it
was accomplished to decrease the spin amount when hit by a driver,
which improved the flight distance, by forming the cover from
polyurethane material as a main component; and to improve the
controllability at approach shot by satisfying the above
correlation represented by the following formula:
(Central point hardness of the core)<(Surface hardness of the
core)<(Intermediate layer hardness)<(Cover hardness)
[0022] Moreover, in the present invention, it was accomplished to
impart the golf ball to excellent scuff resistance by using a
urethane cover having higher hardness than the conventional
urethane cover. Therefore, even if the cover is thin, the
durability of the resulting golf ball can be sufficiently
obtained.
[0023] In order to put the present invention into a more suitable
practical application, it is preferable that
[0024] the golf ball have a deformation amount of 3.0 to 4.0 mm,
when applying from an initial load of 98 N to a final load of 1274
N; and
[0025] the polyurethane material comprise polyurethane-based
thermoplastic elastomer as a main component.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The multi-piece solid golf ball of the present invention
will be explained with reference to the accompanying drawing in
detail. FIG. 1 is a schematic cross section illustrating one
embodiment of the multi-piece solid golf ball of the present
invention. As shown in FIG. 1, the golf ball of the present
invention comprises a core 4 composed of a center 1 and at least
one intermediate layer 2 formed on the center, and a cover 3
covering the core. The intermediate layer 2 may have single-layer
structure or multi-layer structure, which has two or more layers.
In FIG. 1, in order to explain the golf ball of the present
invention simply, a golf ball having one layer of intermediate
layer 2, that is, a three-piece solid golf ball will be used
hereinafter for explanation. The center 1 of the golf ball of the
present invention is obtained by press-molding a rubber composition
under applied heat using a method and condition, which has been
conventionally used for preparing cores of solid golf balls. The
rubber composition comprises a base rubber, a co-crosslinking
agent, an organic peroxide, a filler and the like.
[0027] The base rubber used in the present invention may be also
the same one that has been conventionally used for solid golf
balls, but preferred is polybutadiene rubber, particularly
so-called high-cis polybutadiene rubber containing a cis-1, 4 bond
of not less than 40%, preferably not less than 80%. The high-cis
polybutadiene rubber may be optionally mixed with natural rubber,
polyisoprene rubber, styrene-butadiene rubber,
ethylene-propylene-diene rubber (EPDM) and the like.
[0028] Examples of the co-crosslinking agents are not limited, but
include .alpha.,.beta.-unsaturated carboxylic acids having 3 to 8
carbon atoms (such as acrylic acid, methacrylic acid, etc.) or mono
or divalent metal salts (such as zinc or magnesium salts) thereof,
or a combination thereof. Preferred is zinc acrylate or zinc
methacrylate, because they impart high rebound characteristics to
the resulting golf ball. The amount of the co-crosslinking agent is
preferably from 10 to 40 parts by weight, more preferably from 10
to 35 parts, most preferably from 15 to 30 parts by weight, based
on 100 parts by weight of the base rubber. When the amount of the
co-crosslinking agent is smaller than 10 parts by weight, the
center is not sufficiently crosslinked, and the rebound
characteristics and the durability are degraded. On the other hand,
when the amount of the co-crosslinking agent is larger than 40
parts by weight, the center is too hard, and the shot feel of the
resulting golf ball is hard and poor.
[0029] Examples of the organic peroxides include dicumyl peroxide,
1,1-bis (t-butylperoxy)-3,3,5-trimethylcyclohexane,
2,5-dimethyl-2,5-di(t-butylpe- roxy) hexane, di-t-butyl peroxide
and the like. The preferred organic peroxide is dicumyl peroxide.
The amount of the organic peroxide is preferably from 0.1 to 3.0
parts by weight, more preferably from 0.3 to 2.5 parts by weight,
most preferably from 0.5 to 2.0 parts by weight based on 100 parts
by weight of the base rubber. When the amount of the organic
peroxide is smaller than 0.1 parts by weight, the center is not
sufficiently vulcanized. On the other hand, when the amount of the
organic peroxide is larger than 3.0 parts by weight, the center is
hard, but the rebound characteristics are not sufficiently
improved. In addition, the shot feel is poor.
[0030] The filler, which can be typically used for the core of
solid golf ball, includes for example, inorganic filler (such as
zinc oxide, barium sulfate, calcium carbonate, magnesium oxide and
the like), high specific gravity metal powder filler (such as
tungsten powder, molybdenum powder and the like), and the mixture
thereof. The amount of the filler is preferably from 1 to 30 parts
by weight, more preferably from 3 to 20 parts by weight, based on
100 parts by weight of the base rubber. When the amount of the
filler is smaller than 1 part by weight, it is difficult to adjust
the weight of the resulting golf ball. On the other hand, when the
amount of the filler is larger than 30 parts by weight, the weight
ratio of the rubber component in the center is small, and the
rebound characteristics of the resulting golf ball are degraded too
much.
[0031] Where appropriate, it is possible to compound a component
which is typically used in the manufacture of solid golf ball cores
together with the rubber composition; e.g., other additives such as
organic sulfides, antioxidants and the like. If used, preferably
the amount of the additives is preferably 0.5 to 5.0 parts by
weight, more preferably 0.7 to 4.0 parts by weight, based on 100
parts by weight of the base rubber.
[0032] The center 1 used for the golf ball of the present invention
can be obtained by mixing, and then vulcanizing and press-molding
the above rubber composition under applied heat in a mold. The
vulcanization condition is not limited, but the vulcanization may
be conducted at 140 to 180.degree. C. and 2.8 to 11.8 MPa for 10 to
60 minutes.
[0033] In the golf ball of the present invention, it is suitable
for the center 1 to have a diameter of 25 to 41 mm, preferably 27
to 40 mm. When the diameter of the center 1 is smaller than 25 mm,
it is required to increase the thickness of the intermediate layer
or the cover, and the rebound characteristics of the resulting golf
ball are degraded. On the other hand, when the diameter of the
center is larger than 41 mm, the thickness of the intermediate
layer is too small, and it is difficult to mold the intermediate
layer.
[0034] In the golf ball of the present invention, it is desired for
the center 1 to have a deformation amount when applying from an
initial load of 98 N to a final load of 1274 N of 3.5 to 5.5 mm,
preferably 3.5 to 5.0 mm, more preferably 3.8 to 4.8 mm, most
preferably 4.0 to 4.5 mm. When the deformation amount of the center
is smaller than 3.5 mm, the center is too hard, and the shot feel
of the resulting golf ball is hard and poor. On the other hand,
when the deformation amount is larger than 5.5 mm, the center is
too soft, and the shot feel of the resulting golf ball is heavy and
poor.
[0035] In the present invention, assuming that a central point
hardness of the center, a surface hardness of the center, a
hardness of the intermediate layer and a hardness of the cover in
Shore D hardness are represented by HM, Hs, H.sub.I and H.sub.C,
respectively, it is required for the golf ball to satisfy a
correlation represented by the following formula:
H.sub.M<H.sub.S<H.sub.I<H.sub.C Therefore, in the center 1
of the golf ball of the present invention, it is required that the
surface hardness (H.sub.S) is higher than the central point
hardness (H.sub.M), and the hardness difference thereof
(H.sub.S-H.sub.M) is preferably 5 to 30, more preferably 8 to 30,
most preferably 10 to 25. When the surface hardness is not more
than the central point hardness, the hardness distribution such
that the outer portion is hard and the inner portion is soft in the
whole golf ball are not obtained, and the spin amount is large,
which reduces the flight distance. In addition, when the hardness
difference is smaller than 5, the technical effects accomplished by
having hardness distribution such that the outer portion is hard
and the inner portion is soft in the whole golf ball are not
sufficiently obtained, and the spin amount is large, which reduces
the flight distance. On the other hand, when the hardness
difference is larger than 30, the durability is poor.
[0036] In the golf ball of the present invention, it is desired for
the center 1 to have a central point hardness (H.sub.M) in Shore D
hardness of 20 to 40, preferably 22 to 38, more preferably 25 to
35. When the central point hardness is lower than 20, the center is
too soft, and the rebound characteristics of the resulting golf
ball are degraded, which reduces the flight distance. On the other
hand, the central point hardness is higher than 40, it is difficult
to satisfy the correlation represented by the above formula, and
the hardness distribution such that the outer portion is hard and
the inner portion is soft in the whole golf ball are not obtained.
Therefore, the spin amount is large, which reduces the flight
distance. The term "a central point hardness of the center" as used
herein refers to the hardness, which is determined by cutting the
resulting center into two equal parts and then measuring a hardness
at its central point in section.
[0037] In the golf ball of the present invention, it is desired for
the center 1 to have the surface hardness (H.sub.S) in Shore D
hardness of 35 to 55, preferably 38 to 52, more preferably 40 to
50. When the surface hardness is lower than 35, the center is too
soft, and the rebound characteristics of the resulting golf ball
are degraded, which reduces the flight distance. On the other hand,
when the surface hardness is higher than 55, the intermediate layer
and cover are too hard in order to satisfy the correlation
represented by the above formula, and the shot feel of the
resulting golf ball is poor. The term "a surface hardness of the
center" as used herein refers to the hardness, which is determined
by measuring a hardness at the surface of the resulting center. The
intermediate layer 2 is then formed on the center 1.
[0038] The intermediate layer 2 of the golf ball of the present
invention may be formed from the rubber composition as used for the
center 1, or from thermoplastic resin as a base resin. Examples of
the thermoplastic resins include one or combination of two or more
selected from the group consisting of ionomer resin and
thermoplastic elastomer, which can be typically used for the cover
of golf balls. Examples of the thermoplastic elastomers include
polyester-based thermoplastic elastomer, polyamide-based
thermoplastic elastomer, polyurethane-based thermoplastic
elastomer, polyolefin-based thermoplastic elastomer, styrene-based
thermoplastic elastomer and the like. The thermoplastic elastomers
may have functional groups, such as carboxyl group, glycydyl group,
sulfone group, epoxy group and the like.
[0039] When using the rubber composition for the intermediate layer
2, the amount of the co-crosslinking agent and organic peroxide is
slightly different from the rubber composition used for the center
1 in order to satisfy the correlation represented by the above
formula. That is, the amount of the co-crosslinking agent is
preferably from 15 to 50 parts by weight, more preferably from 20
to 45 parts by weight, based on 100 parts by weight of the base
rubber. Preferred are zinc acrylate, zinc methacrylate, magnesium
acrylate or magnesium methacrylate. The amount of the organic
peroxide is preferably from 0.1 to 6.0 parts by weight, more
preferably from 0.3 to 5.0 parts by weight, most preferably from
0.5 to 4.0 parts by weight based on 100 parts by weight of the base
rubber.
[0040] The ionomer resin may be a copolymer of .alpha.-olefin and
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms, of which a portion of carboxylic acid groups is neutralized
with metal ion, a terpolymer of .alpha.-olefin,
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms and .alpha.,.beta.-unsaturated carboxylic acid ester, of
which a portion of carboxylic acid groups is neutralized with metal
ion or mixture thereof. Examples of the .alpha.-olefins in the
ionomer preferably include ethylene, propylene and the like.
Examples of the .alpha.,.beta.-unsaturated carboxylic acid in the
ionomer include acrylic acid, methacrylic acid, fumaric acid,
maleic acid, crotonic acid and the like, preferred are acrylic acid
and methacrylic acid. Examples of the .alpha.,.beta.-unsaturated
carboxylic acid ester in the ionomer include methyl ester, ethyl
ester, propyl ester, n-butyl ester and isobutyl ester of acrylic
acid, methacrylic acid, fumaric acid, maleic acid, crotonic acid
and the like. Preferred are acrylic acid esters and methacrylic
acid esters. The metal ion, which neutralizes a portion of
carboxylic acid groups of the copolymer or terpolymer, includes an
alkali metal ion, such as a sodium ion, a potassium ion, a lithium
ion and the like; a divalent metal ion, such as a zinc ion, a
calcium ion, a magnesium ion and the like; a trivalent metal ion,
such as an aluminum, a neodymium ion and the like; and mixture
thereof. Preferred are sodium ions, zinc ions, lithium ions and the
like, in view of rebound characteristics, durability and the
like.
[0041] The ionomer resin is not limited, but examples thereof will
be shown by a trade name thereof. Examples of the ionomer resins,
which are commercially available from Du Pont-Mitsui Polychemicals
Co., Ltd. include Hi-milan 1555, Hi-milan 1557, Hi-milan 1601,
Hi-milan 1605, Hi-milan 1652, Hi-milan 1702, Hi-milan 1705,
Hi-milan 1706, Hi-milan 1707, Hi-milan 1855, Hi-milan 1856,
Hi-milan AM7316 and the like. Examples of the ionomer resins, which
are commercially available from Du Pont Co., include Surlyn 8945,
Surlyn 9945, Surlyn 6320, Surlyn 8320, Surlyn AD8511, Surlyn AD8512
and the like. Examples of the ionomer resins, which are
commercially available from Exxon Chemical Co., include Iotek 7010,
Iotek 8000 and the like. These ionomer resins may be used alone or
in combination.
[0042] Examples of the thermoplastic elastomers, which are
commercially available, include polyester-based thermoplastic
elastomer, which is commercially available from Toray-Do Pont Co.,
Ltd. under the trade name of "Hytrel" (such as "Hytrel 3548",
"Hytrel 4047"); polyamide-based thermoplastic elastomer, which is
commercially available from Atofina Japan Co., Ltd. under the trade
name of "Pebax" (such as "Pebax 2533"); polyurethane-based
thermoplastic elastomer, which is commercially available from BASF
Japan Co., Ltd. under the trade name of "Elastollan" (such as
"Elastollan ET880"); olefin-based thermoplastic elastomer available
from Mitsubishi Chemical Co., Ltd. under the trade name "Thermoran"
(such as "Thermoran 3981N"); polyolefin-based thermoplastic
elastomer, which is commercially available from Sumitomo Chemical
Co., Ltd. under the trade name of "Sumitomo TPE" (such as "Sumitomo
TPE3682" and "Sumitomo TPE9455"); styrene-based thermoplastic
elastomer, which are commercially available from Mitsubishi
Chemical Co., Ltd. under the trade name of "Rabalon" (such as
"Rabalon SR04"); styrene-based thermoplastic elastomer available
from Asahi Kasei corporation under the trade name "Tuftec" (such as
"Tuftec H1051"); and the like.
[0043] The composition for the intermediate layer 2 used in the
present invention may optionally contain fillers, pigments and the
other additives such as an antioxidant in addition to the
thermoplastic resin as a base resin.
[0044] Examples of the fillers include inorganic filler (such as
zinc oxide, barium sulfate, calcium carbonate and the like), high
specific gravity metal powder filler (such as tungsten powder,
molybdenum powder and the like), and the mixture thereof.
[0045] The intermediate layer 2 of the present invention may be
formed by conventional methods, which have been known in the art
and used for forming the cover of the golf balls. When the
intermediate layer 2 is formed from the rubber composition, the
rubber composition for the intermediate layer is mixed, and coated
on the center 1 into a concentric sphere, and then vulcanized by
press-molding at 160 to 180.degree. C. for 10 to 20 minutes in the
mold to obtain a core 4, which is formed by covering the
intermediate layer 2 on the center 1. When the intermediate layer 2
is formed from thermoplastic resin, the resin composition for the
intermediate layer is molded into a semi-spherical half-shell, and
the center is covered with the two half-shells, followed by
pressure molding; or the resin composition for the intermediate
layer is injection molded directly on the center 1; to obtain the
core 4. It is preferable for the surface of the resulting core to
be buffed to improve the adhesion to the cover formed on the
core.
[0046] In the present invention, assuming that a central point
hardness of the center, a surface hardness of the center, a
hardness of the intermediate layer and a hardness of the cover in
Shore D hardness are represented by H.sub.M, H.sub.S, H.sub.I and
H.sub.C, respectively, it is required for the golf ball to satisfy
a correlation represented by the following formula:
H.sub.M<H.sub.S<H.sub.I<H.sub.C as described above.
Therefore, in the golf ball of the present invention, it is
required that the hardness (H.sub.I) of the intermediate layer 2 is
higher than the surface hardness (H.sub.S) of the center 1, and the
hardness difference thereof (H.sub.I-H.sub.S) is preferably 1 to
15, more preferably 2 to 10, most preferably 3 to 8. When the
hardness (H.sub.I) of the intermediate layer 2 is not more than the
surface hardness (H.sub.S) of the center 1, the hardness
distribution such that the outer portion is hard and the inner
portion is soft in the whole golf ball are not obtained, and the
spin amount is large, which reduces the flight distance. In
addition, when the hardness difference is smaller than 1, the
technical effects accomplished by having hardness distribution such
that the outer portion is hard and the inner portion is soft in the
whole golf ball are not sufficiently obtained, and the spin amount
is large, which reduces the flight distance. On the other hand,
when the hardness difference is larger than 15, the intermediate
layer is too hard, and the controllability and shot feel of the
resulting golf ball are degraded.
[0047] In the golf ball of the present invention, it is desired for
the intermediate layer 2 to have a hardness (H.sub.I) in Shore D
hardness of 38 to 58, preferably 40 to 55, more preferably 42 to
52. When the hardness of the intermediate layer is lower than 38,
the core is too soft, and the rebound characteristics and
durability of the resulting golf ball are degraded. On the other
hand, the hardness of the intermediate layer is higher than 58, the
shot feel of the resulting golf ball is poor. In addition, the
cover is too hard in order to satisfy the correlation represented
by the above formula, and the controllability at approach shot of
the resulting golf ball is degraded.
[0048] It is desired for the intermediate layer 2 to have a
thickness, which is determined by the diameter of the center 1 and
core 4, of 0.5 to 4.0 mm, preferably 0.5 to 3.0 mm, more preferably
0.7 to 2.0 mm. When the thickness of the intermediate layer is
smaller than 0.5 mm, the technical effects accomplished by the
presence of the intermediate layer are not sufficiently obtained,
and the rebound characteristics are degraded and the spin amount is
increased, which reduces the flight distance. On the other hand,
when the thickness is larger than 4.0 mm, the shot feel of the
resulting golf ball is hard and poor, because the intermediate
layer is relatively hard. The cover 3 is then formed on the
intermediate layer 2.
[0049] In the golf ball of the present invention, it is suitable
for the core 4 to have a diameter of 39.0 to 42.2 mm, preferably
40.0 to 42.0 mm, more preferably 40.5 to 42.0 mm. When the diameter
of the core is smaller than 39.0 mm, the cover is thick, and the
rebound characteristics of the resulting golf ball are degraded. On
the other hand, when the diameter of the core is larger than 42.2
mm, the cover is too thin, and the technical effects accomplished
by the presence of the cover are not sufficiently obtained. In
addition, it is difficult to mold the cover.
[0050] In the golf ball of the present invention, it is desired for
the core 4 to have a deformation amount when applying from an
initial load of 98 N to a final load of 1274 N of 3.2 to 5.0 mm,
preferably 3.2 to 4.8 mm, more preferably 3.4 to 4.5 mm, most
preferably 3.2 to 3.8 mm. When the deformation amount of the core
is smaller than 3.2 mm, the shot feel of the resulting golf ball is
hard and poor. On the other hand, when the deformation amount is
larger than 5.0 mm, the core is too soft, and the shot feel of the
resulting golf ball is heavy and poor.
[0051] The cover 3 is then covered on the core 4. In the golf ball
of the present invention, it is required for the cover 3 to be
formed from polyurethane material as a main component. In the
polyurethane materials, there are thermosetting type and
thermoplastic type polyurethane materials, but preferred are
thermoplastic type polyurethane materials, such as
polyurethane-based thermoplastic elastomer, in view of
processability and cost.
[0052] Polyurethane-based thermoplastic elastomer generally
contains polyurethane structure as hard segment and polyester or
polyether as soft segment. The polyurethane structure generally
contains diisocyanate and curing agent, such as amine-based curing
agent. The polyurethane-based thermoplastic elastomer includes
polyurethane-based thermoplastic elastomer that the diisocyanate is
aromatic diisocyanate, cycloaliphatic diisocyanate or aliphatic
diisocyanate.
[0053] Examples of the aromatic diisocyanate include tolylene
diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI),
1,5-naphthylene diisocyanate (NDI), tolidine diisocyanate (TODI),
xylylene diisocyanate (XDI) and the like. Preferred is MDI.
Concrete examples of the polyurethane-based thermoplastic elastomer
formed by using the MDI include polyurethane-based thermoplastic
elastomer, which is commercially available from BASF Japan Co.,
Ltd. under the trade name of "Elastollan ET890", and the like.
[0054] Examples of the cycloaliphatic diisocyanates include
4,4'-dicyclohexylmethane diisocyanate (H.sub.12MDI), which is
hydrogenated compound of MDI; 1,3-bis(isocyanatomethyl)cyclohexane
(H.sub.6XDI), which is hydrogenated compound of XDI; isophorone
diisocyanate (IPDI); and trans-1,4-cyclohexane diisocyanate (CHDI).
Preferred is the H.sub.12MDI in view of general-purpose properties
and processability. Concrete examples of the polyurethane-based
thermoplastic elastomer formed by using the H.sub.12MDI include
polyurethane-based thermoplastic elastomers, which are commercially
available from BASF Japan Co., Ltd. under the trade name of
"Elastollan XNY90A", "Elastollan XNY97A", "Elastollan XNY585",
"Elastollan XKP016", and the like.
[0055] Examples of the aliphatic diisocyanates include
hexamethylene diisocyanate (HDI), lysine diisocyanate (LDI), and
the like. Preferred is HDI. Concrete examples of the
polyurethane-based thermoplastic elastomer formed by using the HDI
include polyurethane-based thermoplastic elastomer, which is
commercially available from Dainippon Ink & Chemicals Inc.
under the trade name of "Pandex T-7890"(trade name), and the
like.
[0056] Preferred are polyurethane-based thermoplastic elastomers
formed by using diisocyanate having no double bond in backbone
structure in molecule, that is, aliphatic diisocyanate and
cycloaliphatic diisocyanate in view of yellowing resistance.
Preferred are polyurethane-based thermoplastic elastomers formed by
using cycloaliphatic diisocyanate and aromatic diisocyanate, which
have high mechanical strength, in view of scuff resistance.
Therefore, in the present invention, preferred is
polyurethane-based thermoplastic elastomer formed by using
cycloaliphatic diisocyanate in view of both the yellowing
resistance and scuff resistance.
[0057] For the cover 3 of the golf ball of the present invention,
the above polyurethane-based thermoplastic elastomer may be used
alone, or the polyurethane-based thermoplastic elastomer may be
used in combination with at least one of the ionomer resin and the
thermoplastic elastomer as used for the intermediate layer 2. When
using the combination, polyamide-based thermoplastic elastomer is
most preferable in view of the compatibility with the
polyurethane-based thermoplastic elastomer and the rebound
characteristics, and a weight ratio (a/b) of the polyurethane-based
thermoplastic elastomer (a) to the polyamide-based thermoplastic
elastomer (b) is preferably 95/5 to 70/30.
[0058] In the golf ball of the present invention, the cover
composition may optionally contain fillers such as barium sulfate,
pigments such as titanium dioxide, and other additives (such as a
dispersant, an antioxidant, a UV absorber, a photostabilizer and a
fluorescent agent or a fluorescent brightener, etc.), in addition
to the base resin as a main component, as long as the addition of
the additive does not deteriorate the desired performance of the
golf ball cover. If used, the amount of the pigment is preferably
0.1 to 5.0 parts by weight, based on the 100 parts by weight of the
base resin of the cover.
[0059] In the golf ball of the present invention, it is desired for
the cover 3 to have a thickness of 0.3 to 2.0 mm, preferably 0.3 to
1.5 mm, more preferably 0.5 to 1.0 mm. When the thickness of the
cover is smaller than 0.3 mm, the technical effects accomplished by
the presence of the cover are not sufficiently obtained, and the
controllability and durability are degraded. On the other hand,
when the thickness is larger than 2.0 mm, the technical effects
accomplished by the presence of the core and intermediate layer are
not sufficiently obtained, and the rebound characteristics of the
resulting golf ball are degraded, which reduces the flight
distance.
[0060] In the present invention, assuming that a central point
hardness of the center, a surface hardness of the center, a
hardness of the intermediate layer and a hardness of the cover in
Shore D hardness are represented by H.sub.M, H.sub.S, H.sub.I and
H.sub.C, respectively, it is required for the golf ball to satisfy
a correlation represented by the following formula:
H.sub.M<H.sub.S<H.sub.I<H.sub.C as described above.
Therefore, in the golf ball of the present invention, it is
required that the hardness (H.sub.C) of the cover is higher than
the hardness (H.sub.I) of the intermediate layer 2, and the
hardness difference thereof (H.sub.C-H.sub.I) is preferably 1 to
15, more preferably 3 to 12, most preferably 5 to 10. When the
hardness (H.sub.C) of the cover 3 is not more than the hardness
(H.sub.I) of the intermediate layer 2, the hardness distribution
such that the outer portion is hard and the inner portion is soft
in the whole golf ball are not obtained, and the spin amount is
large, which reduces the flight distance. In addition, when the
hardness difference is smaller than 1, the technical effects
accomplished by having hardness distribution such that the outer
portion is hard and the inner portion is soft in the whole golf
ball are not sufficiently obtained, and the spin amount is large,
which reduces the flight distance. On the other hand, when the
hardness difference is larger than 15, the cover is too hard, and
the controllability and shot feel of the resulting golf ball are
degraded.
[0061] In the golf ball of the present invention, it is desired for
the cover 3 to have a hardness (H.sub.C) in Shore D hardness of 45
to 60, preferably 47 to 60, more preferably 50 to 58. When the
hardness of the cover is lower than 45, the deformation amount of
the surface of the resulting golf ball at the time of hitting is
large even if adjusting the hardness of the core, and the rebound
characteristics are degraded, which reduces the flight distance. In
addition, the durability is poor. The term "a hardness of the
intermediate layer" and "a hardness of the cover" as used herein
refer to the hardness, which is determined by measuring a hardness
using a sample of a stack of the three or more heat and press
molded sheets having a thickness of about 2 mm from the resulting
compositions for the intermediate layer and cover, which had been
stored at 23.degree. C. for 2 weeks.
[0062] The cover of the present invention may be formed by the same
methods as used in the intermediate layer. At the time of molding
the cover, many depressions called "dimples" are formed on the
surface of the golf ball. The term "an area of the dimple" as used
herein refers to the area enclosed in the periphery (edge) of the
dimple when observing the central point of the golf ball from
infinity, which is the area of plane. When the dimple is spherical,
the area of the dimple S is determined by calculating from the
following formula:
S=.pi.(d/2).sup.2
[0063] wherein "d" is a diameter of the dimple. The ratio of the
golf ball surface occupied by the dimple to the total surface area
of the golf ball is determined by calculating a ratio of (the total
of the area "S" of each dimple) to (the-surface area of the
phantom-sphere assuming that the golf ball is a true sphere having
no dimples on the surface thereof).
[0064] In the golf ball of the present invention, it is desired for
the dimple to have a ratio of the golf ball surface occupied by the
dimple of 70 to 90%, preferably 72 to 88%, more preferably 74 to
86%, based on the total surface area of the golf ball. When the
ratio of the golf ball surface occupied by the dimple is smaller
than 70%, the technical effects of improving the flight distance
accomplished by the presence of the dimple are not sufficiently
obtained, which reduces the flight distance. On the other hand,
when the ratio of the golf ball surface occupied by the dimple is
larger than 90%, the depressions on the surface of the golf ball
are too many, and the shape of the golf ball is not spherical to
break symmetry of airflow around the golf ball on the fly. In
addition, since there is not sufficient space between dimples
adjacent to each other on the surface of the golf ball, it is
difficult to design the dimples having the ratio of the golf ball
surface occupied by the dimples of larger than 90%. The total
volume of the dimples and the ratio of the golf ball surface
occupied by the dimples as used herein are determined by measuring
at the surface of the resulting golf ball, and if paint is applied
on the cover, they are determined by measuring at the surface of
the applied golf ball.
[0065] In the golf ball of the present invention, it is desired for
the dimple to have total number of 250 to 500, preferably 300 to
480, more preferably 320 to 450. When the total number of the
dimples is smaller than 250, the technical effects accomplished by
the presence of the dimples are not sufficiently obtained. On the
other hand, when the total number of the dimples is larger than
500, the size of each dimple is small, and the technical effects
accomplished by the presence of the dimples are not sufficiently
obtained. Therefore, in the both cases, the technical effects
accomplished by the presence of the dimples are not sufficiently
obtained to improve the flight performance.
[0066] Furthermore, paint finishing or marking with a stamp may be
optionally provided after the cover is molded for commercial
purposes.
[0067] In the golf ball of the present invention, it is desired to
have a deformation amount when applying from an initial load of 98
N to a final load of 1274 N of 3.0 to 4.0 mm, preferably 3.0 to 3.8
mm, more preferably 3.2 to 3.8 mm. When the deformation amount is
smaller than 3.0 mm, the golf ball is too hard, and the shot feel
is hard and poor. On the other hand, when the deformation amount is
larger than 4.0 mm, the golf ball is too soft, and the rebound
characteristics are degraded, which reduces the flight
distance.
[0068] The multi-piece solid golf ball of the present invention is
formed to a diameter of at least 42.67 mm (preferably 42.67 to
42.82 mm) and a weight of no more than 45.93 g, in accordance with
the regulations for golf balls.
[0069] The diameter of golf balls is limited to not less than 42.67
mm in accordance with the regulations for golf balls as described
above. Generally, when the diameter of the golf ball is large, air
resistance of the golf ball on the fly is large, which reduces the
flight distance. Therefore, most of golf balls commercially
available are designed to have a diameter of 42.67 to 42.82 mm. The
present invention is applicable to the golf balls having the
diameter. There are golf balls having large diameter in order to
improve the easiness of hitting. In addition, there are cases where
golf balls having a diameter out of the regulations for golf balls
are required depending on the demand and object of users.
Therefore, it can be considered for golf balls to have a diameter
of 42 to 44 mm, more widely 40 to 45 mm. The present invention is
also applicable to the golf balls having the diameter.
EXAMPLES
[0070] The following Examples and Comparative Examples further
illustrate the present invention in detail but are not to be
construed to limit the scope of the present invention.
[0071] Production of Core
[0072] (i) Production of Center
[0073] The rubber compositions for the center having the
formulations shown in Table 1 were mixed, and then vulcanized by
press-molding at 160.degree. C. for 20-minutes in a mold to obtain
spherical centers. The diameter, deformation amount, the central
point hardness and the surface hardness of the resulting center
were measured. The results are shown in Table 4 (Examples) and
Table 5 (Comparative Examples). Test methods are described
later.
1 TABLE 1 (parts by weight) Center composition I II III BR-11 *1
100 100 100 Zinc acrylate 26 24 20 Zinc oxide 5 5 5 Dicumyl
peroxide 0.7 0.7 0.7 Diphenyl disulfide 0.5 0.5 0.5 Barium sulfate
*2 proper proper proper amount amount amount *1: High-cis
Polybutadiene rubber available from JSR Co., Ltd. *2: The amount of
barium sulfate was adjusted to a proper amount such that the weight
of the resulting golf ball was 45.4 g.
[0074] (ii) Preparation of Intermediate Layer Composition
[0075] The formulation materials shown in Table 2 were mixed using
a kneading type twin-screw extruder to obtain pelletized
intermediate layer compositions. The extrusion condition was,
[0076] a screw diameter of 45 mm,
[0077] a screw speed of 200 rpm, and
[0078] a screw L/D of 35.
[0079] The formulation materials were heated at 200 to 260.degree.
C. at the die position of the extruder. The hardness of the
intermediate layer was measured, using a sample of a stack of the
three or more heat and press molded sheets having a thickness of
about 2 mm from the resulting composition for the intermediate
layer, which had been stored at 23.degree. C. for 2 weeks. The
results are shown in Table 2, Table 4 (Examples) and Table 5
(Comparative Examples).
2 TABLE 2 (parts by weight) Intermediate layer composition A B C D
Hi-milan 1555 *3 -- -- -- 25 Hi-milan 1557 *4 -- -- -- 25 Surlyn
8945 *5 30 25 50 -- Surlyn 9945 *6 30 25 50 -- Rabalon SR04 *7 40
50 -- 50 Shore D hardness 46 43 64 40 *3: Hi-milan 1555 (trade
name), ethylene-methacrylic acid copolymer ionomer resin obtained
by neutralizing with sodium ion, manufactured by Du Pont-Mitsui
Polychemicals Co., Ltd. *4: Hi-milan 1557 (trade name),
ethylene-methacrylic acid copolymer ionomer resin obtained by
neutralizing with zinc ion, manufactured by Du Pont-Mitsui
Polychemicals Co., Ltd. *5: Surlyn 8945 (trade name),
ethylene-methacrylic acid copolymer ionomer resin obtained by
neutralizing with sodium ion, manufactured by Du Pont Co. *6:
Surlyn 9945 (trade name), ethylene-methacrylic acid copolymer
ionomer resin obtained by neutralizing with zinc ion, manufactured
by Du Pont Co. *7: Rabalon SR04 (trade name),
styrene-ethylene-butylene-styrene (SEBS)-based thermoplastic
elastomer, manufactured by Mitsubishi Chemical Co., Ltd.
[0080] (iii) Preparation of Two-Layered Core
[0081] The resulting intermediate layer compositions were directly
injection molded on the center produced in the (ii) to form a
spherical two-layered core. The thickness of the resulting
intermediate layer, the diameter and deformation amount of the
resulting two-layered core were measured, and the results are shown
in Table 4 (Examples) and Table 5 (Comparative Examples).
[0082] Preparation of Cover Composition
[0083] The formulation materials shown in Table 3 were mixed using
a kneading type twin-screw extruder to obtain pelletized cover
compositions. The extrusion condition was,
[0084] a screw diameter of 45 mm,
[0085] a screw speed of 200 rpm, and
[0086] a screw L/D of 35.
[0087] The formulation materials were heated at 200 to 260.degree.
C. at the die position of the extruder. The hardness of the cover
was measured, using a sample of a stack of the three or more heat
and press molded sheets having a thickness of about 2 mm from the
resulting composition for the cover, 5 which had been stored at
23.degree. C. for 2 weeks. The results are shown in Table 3, Table
4 (Examples) and Table 5 (Comparative Examples).
3 TABLE 3 (parts by weight) Cover composition a b c d e Elastollan
XNY97A *8 30 60 -- -- -- Elastollan XNY90A *9 -- -- -- -- 90
Elastollan XKP-016 *10 60 30 -- -- -- Pebax 5533 *11 10 10 -- -- 10
Surlyn 8945 *5 -- -- 50 50 -- Surlyn 9945 *6 -- -- 50 -- -- Surlyn
6320 *12 -- -- -- 50 -- Titanium dioxide 4 4 4 4 4 Shore D hardness
55 52 64 53 42 *8: Elastollan XNY97A (trade name),
polyurethane-based thermoplastic elastomer formed by using
4,4'-dicyclohexylmethane diisocyanate (H.sub.12MDI), commercially
available from BASF Japan Co., Ltd.; Shore A (JIS-A) hardness = 97
*9: Elastollan XNY90A (trade name), polyurethane-based
thermoplastic elastomer formed by using 4,4'-dicyclohexylmethane
diisocyanate (H.sub.12MDI), commercially available from BASF Japan
Co., Ltd.; Shore A (JIS-A) hardness = 90 *10: Elastollan XKP-016
(trade name), polyurethane-based thermoplastic elastomer formed by
using 4,4'-dicyclohexylmethane diisocyanate (H.sub.12MDI),
commercially available from BASF Japan Co., Ltd.; Shore D hardness
= 64 *11: Pebax 2533 (trade name), polyamide-based thermoplastic
elastomer (hard segment: polyamide, commercially available from
Atofina Japan Co., Ltd. *12: Surlyn 6320 (trade name),
ethylene-methacrylic acid-acrylic acid ester terpolymer ionomer
resin obtained by neutralizing with magnesium ion, manufactured by
Du Pont Co.
Examples 1 to 5 and Comparative Examples 1 to 5
[0088] The resulting cover compositions were directly injection
molded on the intermediate layer to form a cover layer having a
thickness shown in Table 4 (Examples) and Table 5 (Comparative
Examples). Then, clear paint was coated on the surface to obtain a
golf ball having a weight of 45.4 g and a diameter of 42.7 mm. The
ratio of the golf ball surface occupied by the dimple was 84% and
the total number of the dimples was 410. With respect to the
resulting golf balls, the deformation amount, flight performance
(spin amount and flight distance) were measured, and the shot feel,
controllability and scuff resistance were evaluated. The results
are shown in Table 6 (Examples) and Table 7 (Comparative Examples).
The test methods are as follows.
(Test Method)
[0089] (1) Deformation Amount of Center
[0090] The deformation amount of center was determined by measuring
a deformation amount when applying from an initial load of 98 N to
a final load of 1274 N on the center.
[0091] (2) Hardness
[0092] (i) Hardness of center
[0093] The surface hardness of the center was determined by
measuring a hardness at the surface of the resulting center. The
central point hardness was determined by cutting the resulting
center into two equal parts and then measuring a hardness at its
central point in section. The hardness was measured using a Shore D
hardness meter according to ASTM D 2240-68.
[0094] (ii) Hardness of Intermediate Layer and Cover
[0095] The hardness of the intermediate layer and cover were
determined by measuring a hardness, using a sample of a stack of
the three or more heat and press molded sheets (slab) having a
thickness of about 2 mm from the intermediate layer composition and
cover composition, which had been stored at 23.degree. C. for 2
weeks, with a Shore D hardness meter according to ASTM D
2240-68.
[0096] (3) Flight Performance
[0097] (i) Flight Performance 1
[0098] After a No. 1 wood club (W#1, a driver) having metal head
was mounted to a swing robot manufactured by Golf Laboratory Co.
and the resulting golf ball was hit at a head speed of 45 m/sec,
the spin amount (backspin amount) immediately after hitting and
flight distance were measured. As the flight distance, total that
is a distance to the stop point of the hit golf ball was measured.
The measurement was conducted 5 times for each golf ball (n=5), and
the average is shown as the result of the golf ball.
[0099] (ii) Flight Performance 2
[0100] After a sand wedge (SW) was mounted to a swing robot
manufactured by Golf Laboratory Co. and the golf ball was hit at a
head speed of 20 m/sec, the launch angle, spin amount and flight
distance were measured. The spin amount (backspin amount)
immediately after hitting was measured. The measurement was
conducted 5 times for each golf ball (n=5), and the average is
shown as the result of the golf ball.
[0101] (4) Shot Feel
[0102] The shot feel of the golf ball is evaluated by 10 golfers
according to a practical hitting test using a No. 1 wood club (W#1,
a driver) having a metal head. The results shown in the Tables
below are based on the fact that most of golfers evaluated with the
same criterion about shot feel. The evaluation criteria are as
follows.
[0103] Evaluation criteria
[0104] .smallcircle.: The golfers felt that the golf ball has good
shot feel such that impact force at the time of hitting is small
and rebound characteristics are good.
[0105] .DELTA.: The golfers felt that the golf ball has fairly good
shot feel.
[0106] x: The golfers felt that the golf ball has poor shot feel
such that impact force at the time of hitting is large or the golf
ball has heavy and poor shot feel.
[0107] (5) Controllability
[0108] The controllability of the golf ball is evaluated by
high-level 10 golfers according to a practical hitting test using a
pitting wedge (PW). The evaluation criteria are as follows. The
results shown in the Tables below are based on the fact that most
of golfers evaluated with the same criterion about
controllability.
[0109] Evaluation Criteria
[0110] .smallcircle.: The golfers felt that it is easy to apply
spin on the golf ball, and the golf ball has good
controllability.
[0111] .DELTA.: The golfers felt that the golf ball has fairly good
controllability.
[0112] x: The golfers felt that it is difficult to apply spin on
the golf ball such that the golf ball slips on the face of golf
club, and the golf ball has poor controllability.
[0113] (6) Scuff Resistance
[0114] After a pitching wedge (PW) commercially available was
mounted to a swing robot manufactured by Golf Laboratory Co., two
points on the surface of each golf ball was hit at a head speed of
36 m/sec one time for each point. The two points were evaluated by
checking the surface appearance by visual observation. The
evaluation criteria are as follows.
[0115] Evaluation Criteria
[0116] .smallcircle.: The surface of the golf ball slightly has a
cut, but it is not particularly noticeable.
[0117] .DELTA.: The surface of the golf ball clearly has a cut, and
the surface becomes fluffy.
[0118] x: The surface of the golf ball is considerably chipped off,
and the surface noticeably becomes fluffy.
Test Results
[0119]
4 TABLE 4 Example No. Test item 1 2 3 4 5 (Center) Composition I I
I I II Diameter (mm) 37.7 37.7 36.7 38.5 36.7 Deformation 4.1 4.1
4.2 4.0 4.5 amount (mm) Central point 28 28 28 29 28 hardness
(Shore D) Surface hardness 43 43 42 44 41 (Shore D) (intermediate
layer) Composition A A A A B Thickness (mm) 1.3 1.3 1.6 1.3 1.6
Hardness (Shore D) 46 46 46 46 43 (Core) Diameter (mm) 40.3 40.3
39.9 41.1 40.3 Deformation 3.7 3.7 3.6 3.7 4.1 amount (mm) (Cover)
Composition a b b b b Thickness (mm) 1.2 1.2 1.4 0.8 1.2 Hardness
(Shore D) 55 52 52 52 52
[0120]
5 TABLE 5 Comparative Example No. Test item 1 2 3 4 5 (Center)
Composition I I I II III Diameter (mm) 37.7 37.7 37.7 36.7 37.7
Deformation 4.1 4.1 4.1 4.1 5.5 amount (mm) Central point 29 29 29
29 26 hardness (Shore D) Surface hardness 43 43 43 43 38 (Shore D)
(intermediate layer) Composition C A A D D Thickness (mm) 1.3 1.3
1.3 1.3 1.3 Hardness (Shore D) 64 46 46 40 40 (Core) Diameter (mm)
40.3 40.3 40.3 40.3 40.3 Deformation 3.3 3.7 3.7 3.8 4.7 amount
(mm) (Cover) Composition a c d b e Thickness (mm) 1.2 1.2 1.2 1.2
1.2 Hardness (Shore D) 55 64 53 52 42
[0121]
6 TABLE 6 Example No. Test item 1 2 3 4 5 (Golf ball) Deformation
3.3 3.4 3.2 3.5 3.8 amount (mm) Flight performance 1 (W#1; 45
m/sec) Spin amount (rpm) 2630 2720 2760 2680 2550 Total (m) 223.5
221.61 222.0 222.7 221.2 Flight performance 2 (SW; 20 m/sec) Spin
amount (rpm) 6460 6620 6710 6600 6530 Shot feel .largecircle.
.largecircle. .largecircle. .largecircle. .DELTA. Controllability
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. Scuff resistance .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle.
[0122]
7 TABLE 7 Comparative Example No. Test item 1 2 3 4 5 (Golf ball)
Deformation 3.0 2.9 3.3 3.4 4.2 amount (mm) Flight performance 1
(W#1; 45 m/sec) Spin amount (rpm) 2820 2650 2750 2900 2850 Total
(m) 220.3 224.5 221.9 217.0 211.3 Flight performance 2 (SW; 20
m/sec) Spin amount (rpm) 6490 4830 6200 6770 6830 Shot feel X X
.largecircle. .DELTA. X Controllability .largecircle. X .DELTA.
.largecircle. .largecircle. Scuff resistance .largecircle.
.largecircle. X .largecircle. .largecircle.
[0123] As is apparent from Tables 6 and 7, the golf balls of
Examples 1 to 5 of the present invention, when compared with the
golf balls of Comparative Examples 1 to 5, had good shot feel,
excellent flight performance and excellent controllability.
[0124] On the other hand, in the golf ball of Comparative Example
1, since the hardness of the intermediate layer is very high, the
hardness distribution such that the outer portion is hard and the
inner portion is soft in the whole golf ball are not obtained, and
the spin amount is large, which reduces the flight distance. In
addition, the impact force at the time of hitting is large, and the
shot feel is poor. In the golf ball of Comparative Example 2, since
the cover is formed from ionomer resin, the cover hardness is high,
and the spin amount is small, which degrades the controllability.
In addition, the impact force is large, and the shot feel is very
poor.
[0125] In the golf ball of Comparative Example 3, since the cover
is formed from the mixture of hard ionomer resin and soft ionomer
resin, the shot feel is good, but the scuff resistance is very
poor. In the golf ball of Comparative Example 4, since the hardness
of the intermediate layer is low, the hardness distribution such
that the outer portion is hard and the inner portion is soft in the
whole golf ball are not obtained, and the spin amount is large,
which reduces the flight distance. In addition, the shot feel is
heavy and poor.
[0126] In the golf ball of Comparative Example 5, since the cover
hardness is low, the deformation amount is large, and the rebound
characteristics are degraded, which reduces the flight distance. In
addition, the shot feel is heavy and poor.
* * * * *