U.S. patent application number 09/466800 was filed with the patent office on 2002-03-28 for solid golf ball.
Invention is credited to MARUKO, TAKASHI, MASUTANI, YUTAKA, NAKAMURA, ATSUSHI, YAMAGISHI, HISASHI.
Application Number | 20020037778 09/466800 |
Document ID | / |
Family ID | 16347462 |
Filed Date | 2002-03-28 |
United States Patent
Application |
20020037778 |
Kind Code |
A1 |
NAKAMURA, ATSUSHI ; et
al. |
March 28, 2002 |
SOLID GOLF BALL
Abstract
A solid golf ball comprises a solid core and a cover of at least
one layer, the solid core having a multilayer construction which
includes a center core and an outer core layer enclosing the center
core. The center core is composed primarily of a thermoplastic
resin or elastomer, and has a diameter of 3-18 mm and a Shore D
hardness of 15-50. The outer core layer has a Shore D hardness near
the interface thereof with the center core which is 1-15 units
higher than the Shore D hardness of the center core. The ball has a
good feel, excellent durability and good distance.
Inventors: |
NAKAMURA, ATSUSHI;
(CHICHIBU-SHI, JP) ; YAMAGISHI, HISASHI;
(CHICHIBU-SHI, JP) ; MARUKO, TAKASHI;
(CHICHIBU-SHI, JP) ; MASUTANI, YUTAKA;
(CHICHIBU-SHI, JP) |
Correspondence
Address: |
SUGHRUE MION ZINN MACPEAK & SEAS
2100 PENNSYLVANIA AVENUE NW
WASHINGTON
DC
200373202
|
Family ID: |
16347462 |
Appl. No.: |
09/466800 |
Filed: |
December 20, 1999 |
Current U.S.
Class: |
473/377 |
Current CPC
Class: |
A63B 37/0075 20130101;
A63B 37/00622 20200801; A63B 37/00621 20200801; A63B 37/0064
20130101; A63B 37/0066 20130101; A63B 37/0059 20130101; A63B 37/06
20130101; A63B 37/0045 20130101; A63B 37/0092 20130101; A63B
37/0003 20130101; A63B 37/04 20130101 |
Class at
Publication: |
473/377 |
International
Class: |
A63B 037/04; A63B
037/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 9, 1999 |
JP |
11-195815 |
Claims
1. A solid golf ball comprising a solid core and a cover of at
least one layer that encloses the solid core, the solid core having
a multilayer construction which includes a center core and an outer
core layer that encloses the center core, wherein the center core
is composed primarily of a thermoplastic resin or a thermoplastic
elastomer, and has a diameter of 3 to 18 mm and a Shore D hardness
of 15 to 50, and the outer core layer has a Shore D hardness near
the interface thereof with the center core which is 1 to 15 units
higher than the Shore D hardness of the center core.
2. The golf ball of claim 1 wherein the outer core layer is made of
a rubber composition composed primarily of
cis-1,4-polybutadiene.
3. The golf ball of claim 1 wherein the outer core layer has a
thickness of 1 to 16 mm.
4. The golf ball of claim 1 wherein at least one layer of the cover
is harder than the outer core layer.
5. The golf ball of claim 1 wherein at least one layer of the cover
is composed primarily of an ionomer resin.
6. The golf ball of claim 1 wherein the center core has a specific
gravity of 0.9 to 1.4.
Description
BACKGROUND OF THE INVENTION
[0001] b 1. Field of the Invention
[0002] The present invention relates to a multilayer golf ball
which has a good durability to repeated impact with a golf club, a
good feel when hit and improved distance.
[0003] b 2. Prior Art
[0004] A variety of multi-piece golf-ball constructions, including
three-piece and four-piece balls, have been developed over the past
few years in order to improve ball performance.
[0005] The practice is known of balancing a soft feel with good
resilience in multi-piece golf balls by giving the ball a hardness
distribution across its respective layers (core, intermediate layer
and cover) in such a way as to retain both properties. In
particular, a number of patents have been described on techniques
for softening the core in order to achieve a soft feel (see, for
example, JP-B 4-55077, JP 2674627, and JP-A 7-194735).
[0006] The cores of the golf balls disclosed in these patents all
have a diameter of about 30 mm, or at least about 20 mm. Softening
the core significantly lowers its resilience, which must then be
compensated for by increasing the hardness of the intermediate
layer and cover, to provide a reasonable resilience for the ball as
a whole. However, increasing the hardness of these layers gives the
ball a poor feel. In addition, stress concentration due to
differences in hardness arises at the interface between the soft
core and the hard intermediate layer, causing the layers to
separate. JP-A 11-417 discloses a core provided with an inner layer
of relatively small diameter. Yet, here too, there exists a large
difference in hardness between the inner layer and the intermediate
layer that has been formed around and encloses the inner layer,
resulting in interfacial adhesion problems such as interlayer
separation, and poor durability due to rubber fissuring in the
intermediate layer.
SUMMARY OF THE INVENTION
[0007] It is therefore an object of the present invention to
provide a solid, multilayer golf ball which has excellent
durability to repeated impact with a golf club, a good feel when
hit and increased distance.
[0008] The invention provides a solid golf ball comprising a solid
core and a cover of at least one layer that encloses the solid
core. The solid core has a multilayer construction which includes a
center core and an outer core layer that encloses the center core.
The center core is composed primarily of a thermoplastic resin or
elastomer, and has a diameter of 3 to 18 mm and a Shore D hardness
of 15 to 50. The outer core layer has a Shore D hardness near the
interface thereof with the center core which is 1 to 15 units
higher than the Shore D hardness of the center core.
[0009] In the solid golf ball of the present invention, the outer
core layer is typically made of a rubber composition composed
primarily of cis-1,4-polybutadiene and has a thickness of 1 to 16
mm. Preferably, at least one layer of the cover is harder than the
outer core layer, and at least one layer of the cover is composed
primarily of an ionomer resin. The center core typically has a
specific gravity of 0.9 to 1.4.
[0010] The invention is directed to a solid golf ball comprising a
solid core enclosed in a cover, wherein the solid core has both a
center core and an outer core layer enclosing the center core. It
has been found that by forming the center core to a small diameter,
setting the Shore D hardness at the surface of the center core at
from 15 to 50, and setting the Shore D hardness difference between
the center core and the inside surface of the outer core layer
within a specific range, the ball can be endowed with an improved
durability to repeated impact with a golf club, a good feel and
increased distance. It has also been found that using a resin
material having a relatively low Shore D hardness in the center
core greatly facilitates the grinding step, making it possible to
efficiently produce small-diameter center cores. Moreover, the
decline in the resilience due to the use of a resin material in the
center core is relatively small for the ball as a whole because of
the small diameter of the center core.
BRIEF DESCRIPTION OF THE DRAWING
[0011] The objects, features and advantages of the invention will
become more apparent from the following detailed description.
[0012] The only FIGURE, FIG. 1 is a sectional view showing a solid
golf ball according to one embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] Referring to FIG. 1, the solid golf ball of the invention is
illustrated as comprising a solid core 1 enclosed within a cover 2.
The solid core 1 has a center core 3 of smaller diameter than in
the prior art, and an outer core layer 4 which encloses the center
core 3 and is itself enclosed by the cover 2. The cover 2 is shown
as a single layer in FIG. 1, but may be composed of two, three or
more layers, if necessary.
[0014] The center core 3 in the present invention is not made of a
rubber composition as in prior-art golf balls. Rather, it is
composed primarily of a thermoplastic resin or elastomer, examples
of which include ionomer resins, thermoplastic polyamide elastomers
and thermoplastic polyester elastomers. Exemplary commercial
products of this type include Surlyn (ionomer resins manufactured
by E.I. DuPont de Nemours and Co.), Himilan (ionomer resins
manufactured by DuPont-Mitsui Polychemicals Co., Ltd.), Amilan
(thermoplastic polyamide elastomers manufactured by Toray
Industries, Inc.), Rilsan (thermoplastic polyamide elastomers
manufactured by DuPont-Toray Co., Ltd.), and Hytrel (thermoplastic
polyester elastomers manufactured by DuPont-Toray Co., Ltd.).
[0015] If desired, an inorganic filler such as barium sulfate,
titanium dioxide or zinc oxide may be blended as a specific gravity
modifier in the resin material. Typically, the amount of filler
blended is not more than 40 parts by weight, and preferably not
more than 38 parts by weight, per 100 parts by weight of the base.
Too much inorganic filler may lower the workability of the resin
material during production of the center core.
[0016] The center core can be produced from a material composed
primarily of the above thermoplastic resin or thermoplastic
elastomer by a known process such as injection molding. The center
core must have a diameter of at least 3 mm, although the diameter
is preferably at least 3.5 mm, more preferably at least 4 mm, even
more preferably at least 5 mm, and most preferably at least 8 mm.
The upper limit in the center core diameter is 18 mm, preferably 16
mm, and most preferably 15 mm. A center core with too small a
diameter fails to achieve the intended effect, whereas too large a
diameter adversely affects the resilience of the ball and causes
rubber fissuring in the surrounding layer, resulting in poor ball
durability.
[0017] The center core has a Shore D hardness of at least 15,
preferably at least 18, more preferably at least 22, and most
preferably at least 25. The upper limit in the Shore D hardness is
50, and preferably 48. Too low a hardness gives the ball poor
resilience, whereas a hardness that is too high results in a hard
feel. The Shore D hardness of the center core, as used herein,
refers to measurements obtained in accordance with ASTM D-2240.
[0018] The specific gravity of the center core is not subject to
any particular limitation, although a specific gravity of 0.90 to
1.40, preferably 0.95 to 1.35, and most preferably 1.00 to 1.30, is
generally recommended. Too low a specific gravity would make it
necessary to increase the specific gravity of the rubber material
used in the outer core layer and compromise the resilience of the
ball. On the other hand, a specific gravity higher than the
foregoing range would require the addition of too much filler to
the center core composition, which can adversely affect
moldability.
[0019] The outer core layer 4 around the center core 3 is
preferably made of a rubber composition to more easily achieve good
ball resilience. Alternatively, use can be made of a thermoplastic
resin or elastomer, suitable examples of which include ionomer
resins, thermoplastic polyamide elastomers and thermoplastic
polyester elastomers.
[0020] When used as the outer core layer, the rubber composition is
preferably one comprising polybutadiene as a base as in
conventional golf ball cores. The use of 1,4-polybutadiene having a
cis structure content of at least 40% is especially suitable. Where
desired, other suitable rubber components such as natural rubber,
polyisoprene rubber or styrene-butadiene rubber may be compounded
in the polybutadiene. The resilience of the ball can be improved by
increasing the proportion of rubber components. The other rubber
components may be compounded in amounts of up to 10 parts by weight
per 100 parts by weight of the polybutadiene.
[0021] A crosslinking agent may be blended in the rubber
composition. Exemplary crosslinking agents are the zinc and
magnesium salts of unsaturated fatty acids (e.g., zinc
methacrylate, zinc acrylate), and ester compounds (e.g.,
trimethylpropane methacrylate). Zinc acrylate is especially
preferred for achieving a high resilience. The crosslinking agent
is preferably included in an amount of about 10 to 40 parts by
weight per 100 parts by weight of the base rubber.
[0022] A vulcanizing agent is generally compounded in the rubber
composition. It is recommended that the vulcanizing agent include a
peroxide. Examples of suitable peroxides include commercially
available products such as Perhexa 3M (manufactured by Nippon Oils
and Fats Co., Ltd.). The amount of vulcanizing agent included in
the rubber composition is preferably from about 0.6 to 2 parts by
weight per 100 parts by weight of the base rubber.
[0023] If necessary, other suitable ingredients may also be added
to the rubber composition, including antioxidants and fillers such
as zinc oxide or barium sulfate for adjusting the specific gravity.
The amount of such specific gravity modifiers blended in the
composition is typically from about 1 to 30 parts by weight per 100
parts by weight of the base rubber.
[0024] If the outer core layer is made of a rubber composition,
production of the layer may be carried out by using a known method
to vulcanize and cure the rubber composition. For example, one
highly suitable method is a two-step process in which the rubber
composition is first subjected to primary vulcanization
(semi-vulcanization) in a mold to form a pair of hemispherical
cups. A pre-formed center core is then placed in one of the
hemispherical cups, the other cup is closed over this, and
secondary vulcanization (full vulcanization) is carried out.
[0025] The outer core layer may be made of a single layer or a
plurality of layers. If it is made of two or more layers, the other
layer or layers may be made of a similar rubber composition or may
be made primarily of a resin, although use of a similar rubber
composition is preferred. The outer core layer is preferably
adjusted to such a thickness that the diameter of the solid core 1
comprising the center core 3 and the outer core layer 4 is
preferably from 34.0 to 41.0 mm, and especially from 34.5 to 40.0
mm.
[0026] In the practice of the invention, it is critical for the
outer core layer side at the interface between the center core and
the outer core layer to have a higher Shore D hardness than the
center core side. Specifically, the outer core layer side must have
a Shore D hardness that is from 1 to 15 units higher. Preferably,
the difference in Shore D hardness is at least 2 units, but not
more than 13 units, and further preferably not more than 10 units.
A center core which is so soft as to make the hardness difference
at the interface with the outer core layer excessive tends to
result in not only a loss of energy and decreased resilience
characteristics, but also a poor durability. The Shore D hardness
of the outer core layer is determined by cutting the golf ball in
half and taking the measurement on the smooth cut face.
[0027] The golf ball of the invention is made by enclosing the
solid core 1 with a cover 2 composed of one or more layers. A known
cover stock material may be used, suitable examples of which
include ionomer resins, balata rubber, and polyurethane-,
polyamide- and polyester-based thermoplastic elastomers. Of these,
ionomer resins are especially preferred. The cover is preferably
formed using a conventional process such as injection molding.
[0028] The thickness or gage of the cover is not critical although
this is generally from 0.8 to 4.3 mm, preferably from 1.0 to 3.5
mm, and most preferably from 1.5 to 2.5 mm. When the cover is
composed of two or more layers, the overall thickness of the
constituent layers should fall within the above range. A cover
which is too thin would reduce the durability of the ball, while
excessive thickness would compromise the feel.
[0029] Preferably, at least one layer of the cover is harder than
the outer core layer. Most often, the cover has a Shore D hardness
of 40 to 70, and preferably from 50 to 68.
[0030] As in conventional golf balls, the golf ball of the
invention has numerous dimples formed on the surface of the cover.
The total number of dimples is preferably from 350 to 500, more
preferably from 370 to 480, and most preferably from 390 to 450.
The dimples may have a geometrical arrangement that is octahedral
or icosahedral, for example. Nor is the dimple pattern limited to a
circular pattern, the use of any other suitable pattern, such as a
square, hexagonal, pentagonal or triangular pattern, also being
acceptable.
[0031] The golf ball of the invention should have a diameter and
weight which conform with the Rules of Golf. That is, the ball
should generally have a diameter large enough to keep it from
passing through a ring with an inside diameter of 42.67 mm.
Preferably, the diameter is from 42.67 mm to 42.75 mm. The ball
should generally have a weight of not more than 45.93 grams, and
preferably from 45.2 to 45.8 grams.
[0032] There has been described a solid golf ball which provides a
good feel when hit with a golf club, excellent durability to
repeated impact, and good distance characteristics.
EXAMPLES
[0033] Examples of the invention and comparative examples are given
below by way of illustration, and are not intended to limit the
invention.
Examples and Comparative Examples
[0034] In most of the examples, center cores having the
specifications shown in Table 1 were produced by injection molding
the resin materials formulated as shown in Table 1 in a mold. In
Comparative Examples 2 and 3, center cores were produced by
vulcanizing the rubber compositions formulated as shown in Table
1.
[0035] An outer core layer was formed in each example by working
the rubber composition shown in Table 1 using a roll mill, then
subjecting the mixed composition to primary vulcanization
(semi-vulcanization) in a mold at 130.degree. C. for 6 minutes,
thereby producing a pair of hemispherical cups. The pair of cups
was closed as the outer core layer over the surface of the center
core, then subjected to secondary vulcanization (full
vulcanization) at 155.degree. C. for 15 minutes, giving a solid
core having a two-layer construction.
[0036] The cover stock shown in Table 1 was injection molded about
the solid core in each example to form a cover bearing dimples of
the same shape, arrangement and number, yielding a solid golf ball
having the characteristics shown in Table 1.
[0037] In Table 1, the Shore D hardness values given for the center
core and the cover were obtained in accordance with ASTM D-2240.
The Shore D hardness values given for the outer core layer were
obtained in each case by cutting the ball in half and measuring the
hardness at a given point on the cut face.
[0038] The properties of the resulting golf balls were measured and
evaluated. Using a swing robot, the ball was hit with a driver at a
head speed of 45 m/s and the carry and total distance were
measured.
[0039] Workability
[0040] The workability of the center core material during the
mixing step was rated as follows.
[0041] Good: Easy to mix
[0042] Fair: Mixing operation was not entirely smooth
[0043] Poor: Difficult to mix
[0044] Feel
[0045] Three professional golfers rated the feel of the golf balls
obtained in each example according to the following criteria.
Results shown in the table are averaged ratings.
[0046] Good: Appropriately soft, yet solid feel
[0047] Fair: Ordinary feel
[0048] Poor: Hard feel
[0049] Durability
[0050] The ball was hit consecutively 50 times with a driver
mounted on a swing robot. Durability was evaluated by measuring the
initial velocity because this value drops off sharply when fissures
form in the rubber at the interior of the ball. The ball was rated
"Poor" when a drop of initial velocity was found and "Good" when no
drop was found until the last strike.
[0051] The results are presented in Table 1.
1 TABLE 1 EX 1 EX 2 EX 3 EX 4 EX 5 CE 1 CE 2 CE 3 Solid Center
Formula- Hytrel 3046 100 100 core core tion (polyester).sup.1)
(pbw) Hytrel 4001 100 100 (polyester).sup.1) Hytrel 4701 100
(polyester).sup.1) Rilsan BMNO 100 (polyamide).sup.2) Barium
sulfate 9 13 10 10 42 cis-l,4-Polybutadiene 100 100 Zinc oxide 5 5
Barium sulfate 68 38 Zinc diacrylate 20 5.0 Dicumyl peroxide 1.2
1.2 Parame- Diameter (mm) 15.0 10.0 8.0 6.0 5.0 22.0 10.0 32.0 tars
Weight (g) 2.03 0.62 0.32 0.14 0.08 7.42 0.73 19.73 Specific
gravity 1.15 1.18 1.20 1.20 1.20 1.33 1.40 1.15 Shore D hardness 31
31 41 41 47 83 48 25 (ASTM-D-2240) Workability during good good
good good good fair poor good mixing Outer Formula
cis-1,4-Polybutadiene 100 100 100 100 100 100 100 100 core tion
Zinc oxide 5 5 5 5 5 5 5 5 layer (pbw) Barium sulfate 29.0 33.0
21.0 20.5 23.0 11.5 21.0 26.0 Zinc diacrylate 10.0 5.0 28.0 30.0
27.0 36.5 27.0 30.0 Dicumyl peroxide 1.2 1.2 1.2 1.2 1.2 1.2 1.2
1.2 Parame- Primary vulcanization 130.degree. C./ 130.degree. C./
130.degree. C./ 130.degree. C./ 130.degree. C./ 130.degree. C./
130.degree. C./ 130.degree. C./ ters conditions 6 min 6 min 6 min 6
min 6 min 6 min 6 min 6 min Secondary 155.degree. C./ 155.degree.
C./ 155.degree. C./ 155.degree. C./ 155.degree. C./ 155.degree. C./
155.degree. C./ 155.degree. C./ vulcanization 15 min 15 min 15 min
15 min 15 min 15 min 15 min 15 min conditions Weight (g) 35.0 35.0
35.0 35.0 35.0 35.0 35.0 35.0 (including center core) Diameter (mm)
38.5 38.5 38.5 38.5 38.5 38.5 38.5 38.5 Interfacial Center core 31
31 41 41 41 83 48 28 hardness Inside of outer 40 35 53 55 54 60 54
55 (Shore D) core layer (Outer core layer) 9 4 12 14 13 -23 6 27
(Center core) Cover Formulation Himilan 1605 50 50 50 (pbw)
(ionomer).sup.3) Himilan 1706 50 50 50 (ionomer).sup.3) Himilan
1557 50 50 50 50 50 (ionomer).sup.3) Himilan 1601 50 50 50 50 50
(ionomer).sup.3) Parameters Shore D hardness 58 58 62 62 58 58 62
58 Thickness (mm) 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 Ball Parameters
Diameter (mm) 42.7 42.7 42.7 42.7 42.7 42.7 42.7 42.7 Weight (g)
45.3 45.3 45.3 45.3 45.3 45.3 45.3 45.3 HS = 45 m/s Carry (m) 215.0
214.5 215.5 213.5 212.0 209.5 210.0 211.0 Total distance (m) 231.0
229.5 230.0 231.5 229.0 225.0 228.0 229.0 Feel good good good good
good good fair good Durability good good good good good poor fair
poor
[0052] 1) thermoplastic polyester elastomers manufactured by
DuPont-Toray Co., Ltd.
[0053] 2) a thermoplastic polyamide elastomer manufactured by
DuPont-Toray Co., Ltd.
[0054] 3) ionomer resins manufactured by DuPont-Mitsui
Polychemicals Co., Ltd.
[0055] Japanese Patent Application No. 11-195815 is incorporated
herein by reference.
[0056] Although some preferred embodiments have been described,
many modifications and variations may be made thereto in light of
the above teachings. It is therefore to be understood that the
invention may be practiced otherwise than as specifically described
without departing from the scope of the appended claims.
* * * * *