U.S. patent application number 09/294205 was filed with the patent office on 2002-03-14 for golf ball.
Invention is credited to MARUKO, TAKASHI, MASUTANI, YUTAKA.
Application Number | 20020032079 09/294205 |
Document ID | / |
Family ID | 14905860 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020032079 |
Kind Code |
A1 |
MARUKO, TAKASHI ; et
al. |
March 14, 2002 |
GOLF BALL
Abstract
In a golf ball comprising a core, an intermediate layer, and a
cover, the core or the cover is provided with a plurality of
protrusions penetrating into the intermediate layer, and the
material of the protrusions has at least 8 units higher Shore D
hardness than the material of the intermediate layer. The
protrusions satisfy the applicable range of Euler's buckling
formula. The golf ball has improved performance.
Inventors: |
MARUKO, TAKASHI;
(CHICHIBU-SHI, JP) ; MASUTANI, YUTAKA;
(CHICHIBU-SHI, JP) |
Correspondence
Address: |
SUGHRUE MION ZINN MACPEAK & SEAS
2100 PENNSYLVANIA AVENUE N W
WASHINGTON
DC
200373202
|
Family ID: |
14905860 |
Appl. No.: |
09/294205 |
Filed: |
April 20, 1999 |
Current U.S.
Class: |
473/373 ;
473/371; 473/378 |
Current CPC
Class: |
A63B 37/0043 20130101;
A63B 37/0003 20130101; A63B 37/0097 20130101 |
Class at
Publication: |
473/373 ;
473/371; 473/378 |
International
Class: |
A63B 037/06; A63B
037/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 1998 |
JP |
10-125267 |
Claims
1. A golf ball comprising a core, an intermediate layer around the
core, and a cover around the intermediate layer, wherein said core
or said cover is integrally provided with a plurality of
protrusions penetrating into the intermediate layer, and the
material of which the protrusions are made has a Shore D hardness
which is at least 8 units higher than the Shore D hardness of the
material of which the intermediate layer is made, each said
protrusion satisfying the relationship:L>.pi.(EI/A.sigma..su-
b.b).sup.1/2wherein L is the length (mm) of the protrusion, E is
the Young's modulus (MPa) of the material of the protrusion, I is
the geometrical moment of inertia (mm.sup.4) of the protrusion, A
is the cross-sectional area (mm.sup.2) of the protrusion, and
.sigma..sub.b is the yield stress (MPa) of the material of the
protrusion.
2. The golf ball of claim 1 wherein said protrusions have a rounded
planar top shape.
Description
[0001] This invention relates to a golf ball comprising a core, an
intermediate layer, and a cover, and more particularly, to such a
golf ball in which the core or the cover is provided with
protrusions penetrating into the intermediate layer.
BACKGROUND OF THE INVENTION
[0002] A variety of studies and proposals have been made to find a
good compromise between flight distance and "feel" of golf balls.
For solid golf balls comprising a solid core and a cover, one
common approach is to construct the core and the cover into
multilayer structures for adjusting their hardness and dimensions
(including diameter and gage).
[0003] For example, U.S. Pat. No. 5,439,227 discloses a three-piece
golf ball comprising a core, a cover inner layer and a cover outer
layer, the cover outer layer being harder than the cover inner
layer. U.S. Pat. No. 5,490,674 discloses a three-piece golf ball
comprising a solid core of inner and outer layers and a cover, the
core inner layer being harder than the core outer layer.
[0004] While the respective layers of most golf balls define smooth
spherical surfaces, the golf balls disclosed in U.S. Pat. Nos.
2,376,085 and 5,692,973 have a core which is provided with
outwardly extending protrusions for preventing the core from being
offset during injection molding of the cover therearound. The
protrusions in these golf balls are substitutes for the support
pins used during injection molding. These patents do not attempt to
positively utilize the shape effect of support pin-substituting
protrusions, but rather intend to avoid incorporation of a distinct
material in the cover by forming the protrusions from the same
material as the cover.
SUMMARY OF THE INVENTION
[0005] An object of the invention is to provide a golf ball
comprising a core, an intermediate layer and a cover wherein the
core or cover is provided with a plurality of protrusions
penetrating into the intermediate layer, thereby achieving a good
compromise between flight distance and control, which has never
been achieved in prior art golf balls.
[0006] The shape effect of respective layers of a golf ball was
investigated. It is well known from the study of strength of
materials that a beam supporting an axial compressive load gives
rise to the buckling phenomenon that as the load increases, uniform
compression becomes unstable and is shifted laterally whereby the
beam is bent. The invention has been devised by applying the
buckling phenomenon to a golf ball. Specifically, in a golf ball
comprising a core, an intermediate layer, and a cover, the core or
the cover is integrally provided with a plurality of protrusions
penetrating into the intermediate layer, and the material of which
the protrusions are made is harder than the material of which the
intermediate layer is made. The protrusions each satisfy the
applicable range of Euler's buckling formula:
L>.pi.(EI/A.sigma..sub.b).sup.1/2
[0007] wherein L is the length (mm) of the protrusion, E is the
Young's modulus (MPa) of the material of the protrusion, I is the
geometrical moment of inertia (mm.sup.4) of the protrusion, A is
the cross-sectional area (mm.sup.2) of the protrusion, and
.sigma..sub.b is the yield stress (MPa) of the material of the
protrusion. Then the buckling phenomenon is applicable to the core
or cover protrusions embedded in the intermediate layer.
[0008] When the ball is struck at a relatively high head speed,
typically with a driver, the protrusions embedded within the
intermediate layer give rise to a buckling phenomenon so that the
ball is substantially deformed, which provides a reduced spin rate
and an increased launch angle, resulting in an increased carry.
When the ball is struck at a relatively low head speed, typically
with a short iron, the protrusions within the intermediate layer
does not give rise to a buckling phenomenon and the ball undergoes
small deformation, which provides an increased backspin rate and
maintains ease of control. With respect to the "feel" of the ball
when hit, the ball gives a soft pleasant feel on driver shots and a
tight full-body feel on short iron shots.
[0009] More particularly, when the ball is struck at a relatively
high head speed as with a driver so that ball is given a large
impact force, that force acts to cause the protrusions to buckle.
On the other hand, when the ball is struck at a relatively low head
speed as with a short iron so that the ball is given a small impact
force, the protrusions do not buckle. In the former case of large
impact force, the protrusions buckle so that the strength of the
protrusions embedded in the intermediate layer does not
substantially act and only the strength of the intermediate layer
formed softer than the protrusions contributes. This results in a
reduced spin rate and an increased carry. In the latter case of
small impact force, the protrusions do not buckle so that the
strength of the intermediate layer in a substantial sense is a
combination of the strength of the intermediate layer in itself and
the strength of the protrusions embedded therein, that is, higher
than the strength of the intermediate layer in itself by a value
attributable to the protrusions of higher hardness. Then the
intermediate layer exhibits a harder behavior, leading to an
increased spin rate. Therefore, in the golf ball having protrusions
of higher hardness penetrating in the intermediate layer according
to the invention, the intermediate layer with protrusions embedded
therein exhibits a different behavior depending on the magnitude of
impact force, that is, the number of golf club.
[0010] Accordingly, the present invention provides a golf ball
comprising a core, an intermediate layer around the core, and a
cover around the intermediate layer. The core or the cover is
integrally provided with a plurality of protrusions penetrating
into the intermediate layer. The material of which the protrusions
are made has a Shore D hardness which is at least 8 units higher
than the Shore D hardness of the material of which the intermediate
layer is made. The protrusions satisfy the applicable range of
Euler's buckling formula. Preferably, the protrusions each have a
rounded planar shape at its top.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic cross-sectional view of a golf ball
according to one embodiment of the invention.
[0012] FIG. 2 is a schematic cross-sectional view of a golf ball
according to another embodiment of the invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0013] Referring to FIGS. 1 and 2, a golf ball according to the
invention, designated at 1, is illustrated as comprising a solid
core 2, an intermediate layer 3 enclosing the core 2, and a cover 4
enclosing the intermediate layer. The core 2 and cover 4 each may
consist of either a single layer or plural layers. All these
components are disposed in a concentric fashion.
[0014] In the golf ball of the invention, the core 2 is integrally
provided with a plurality of outward protrusions 2a penetrating
into the intermediate layer 3 as shown in FIG. 1. Alternatively,
the cover 4 is integrally provided with a plurality of inward
protrusions 4a penetrating into the intermediate layer 3 as shown
in FIG. 2.
[0015] The material of which the protrusions are made (which is
either the core material or the cover material) is harder than the
material of which the intermediate layer is made. Specifically the
Shore D hardness of the material of the protrusions is at least 8
units, preferably 10 to 50 units, higher than the Shore D hardness
of the material of the intermediate layer. With a hardness
difference of less than 8 Shore D units, the boundaries between the
protrusions and the intermediate layer become less definite so that
the shape effect of protrusions becomes weak. The intermediate
layer excluding the protrusions should preferably have a Shore D
hardness of 15 to 55, more preferably 20 to 50.
[0016] The protrusions or protruding columns embedded in the
intermediate layer satisfy the following relation, that is, the
applicable range of Euler's buckling formula used in the
strength-of-materials theory.
L>.pi.(EI/A.sigma..sub.b).sup.1/2
[0017] In the relation, .pi.(EI/A.sigma..sub.b).sup.1/2 is referred
to as a protrusion coefficient. The protrusion coefficient, which
varies with a particular material, should satisfy the relation
representing the applicable range. That is, the protrusion
coefficient should be smaller than the protrusion length L in order
that the invention exert the desired effect.
[0018] Herein, L is the length (mm) of the protrusion, more
particularly, the height of the protrusion or the depth of the
recess, and is usually 1.0 to 6.0 mm, preferably 1.5 to 5.0 mm. A
is the transverse cross-sectional area (mm2) of the protrusion and
is equal to .pi.d.sup.2/4 when the protrusion has a circular cross
section having a diameter d. I is the geometrical moment of inertia
(mm.sup.4) of the protrusion and is equal to .pi.d.sup.4/64 when
the protrusion has a circular cross section having a diameter d. A
transverse cross section of the protrusion has a size of 0.5 to 5.0
mm, preferably 1.0 to 4.0 mm, which size corresponds to a diameter
d when the protrusion has a circular cross section. E is the
Young's modulus (MPa) of the material of the protrusion, and
.sigma..sub.b is the yield stress (MPa) of the material of the
protrusion. E and .sigma..sub.b and may be selected as appropriate
since they differ depending on a particular material used and
cannot be specified. For those materials which do not exhibit the
definite yield stress at which plastic deformation suddenly takes
place, the stress at which the permanent set exceeds 10% may be
used as a substitute for the yield stress .sigma..sub.b.
[0019] As is evident from Euler's buckling formula:
buckling load P.sub.E=.pi..sup.2EI/4L.sup.2
[0020] wherein E, L and I are as defined above, the length of the
protrusion changes its optimum range depending on the physical
properties of the material and the cross-sectional shape. That is,
as the ratio of length to cross-sectional area of the protrusion
becomes higher, the buckling phenomenon takes place more
frequently. If the protrusions are outside the applicable range of
Euler's buckling formula, it becomes impossible that the
protrusions in the intermediate layer undergo the buckling
phenomenon. Then, the deformation of the ball is restrained,
failing to achieve the benefit of the invention that when hit at a
relatively high head speed as with a driver, the ball is
substantially deformed by virtue of the buckling of the protrusions
thereby accomplishing a reduced backspin rate, an increased launch
angle and a drastically increased carry.
[0021] The shape of protrusions is not critical and they may be
formed to an appropriate shape such as prism, cylinder,
frusto-pyramid, or frusto-cone. The top of the protrusion
preferably has a rounded planar shape. Then the protrusion become
more flexible since the boundary conditions become approximate to
fixed end/free end column conditions.
[0022] The total number of protrusions is usually about 80 to about
600, preferably about 90 to about 500. The protrusions are
distributed on the spherical surface of the intermediate layer,
preferably in a well-know symmetric arrangement, for example, a
regular octahedral or regular icosahedral arrangement.
[0023] Since the material of the protrusions extending from the
core or cover into the intermediate layer is harder than the
material of the intermediate layer and falls within the applicable
range of Euler's buckling formula used in the strength-of-materials
theory, there is achieved the benefit of the invention that when
hit at a relatively high head speed as with a driver, the ball is
substantially deformed by virtue of the buckling of the protrusions
thereby accomplishing a reduced backspin rate, an increased launch
angle and a drastically increased carry. When the ball is struck at
a relatively low head speed, typically with a short iron, the
protrusions does not give rise to a buckling phenomenon and the
ball undergoes only small deformation, which provides an increased
backspin rate and maintains ease of control as conventional.
[0024] Now the respective components of the golf ball are
described.
[0025] The solid core 2 may be formed of any desired material
although vulcanizable rubber primarily comprising polybutadiene
rubber, polyisoprene rubber, natural rubber or silicone rubber is
often used. For high resilience, vulcanizable rubber primarily
comprising polybutadiene is preferred.
[0026] In the rubber composition, a crosslinking agent may be
blended with the rubber component. Exemplary crosslinking agents
are zinc and magnesium salts of unsaturated fatty acids such as
zinc methacrylate and zinc acrylate, and esters such as
trimethylpropane methacrylate. Of these, zinc acrylate is preferred
because it can impart high resilience. The crosslinking agent is
preferably used in an amount of about 15 to 40 parts by weight per
100 parts by weight of the base rubber. A vulcanizing agent may
also be blended, preferably in an amount of about 0.1 to 5 parts by
weight per 100 parts by weight of the base rubber. In the rubber
composition, zinc oxide or barium sulfate may be blended as an
antioxidant or specific gravity adjusting filler. The amount of
filler blended is preferably about 5 to 130 parts by weight per 100
parts by weight of the base rubber.
[0027] One preferred formulation of the solid core-forming rubber
composition is given below.
1 Parts by weight Cis-1,4-polybutadiene 100 Zinc oxide 5 to 40 Zinc
acrylate 15 to 40 Barium sulfate 0 to 40 Peroxide 0.1 to 5.0
[0028] Vulcanizing conditions include a temperature of
150.+-.10.degree. C. and a time of about 5 to 20 minutes.
[0029] The rubber composition is obtained by kneading the
above-mentioned components in a conventional mixer such as a
kneader, Banbury mixer or roll mill. The resulting compound is
molded in a mold by injection or compression molding.
[0030] The solid core (excluding the protrusions) is preferably
made to a diameter of 28 to 38 mm, more preferably 30 to 37 mm.
Preferably the core has a Shore D hardness of 20 to 50, more
preferably 25 to 45, and a deflection under a load of 100 kg of 2.5
to 5.0 mm, more preferably 3.0 to 4.5 mm. The weight of the core is
usually about 12 to about 35.0 grams. The core is usually formed to
a single layer structure from one material although it may also be
formed to a multilayer structure of two or more layers of different
materials if desired.
[0031] In one embodiment of the invention wherein protrusions 2a
extend outward from the core 2 into the intermediate layer 3 as
shown in FIG. 1, the core is formed on its outer surface with
protrusions. Specifically, the cavity of a mold for forming the
core is formed on its inner surface with a plurality of recesses
corresponding to the plurality of protrusions. This mold enables
that the core having a plurality of protrusions on its outer layer
be formed by conventional molding. In some cases, protrusions may
be adhesively joined to the core surface.
[0032] The intermediate layer-forming material is then formed
around the core with protrusions by injection or compression
molding whereupon the core protrusions are embedded in the
intermediate layer.
[0033] The material of which the intermediate layer is made is not
critical and may be either a resinous material or a rubbery
material. For durability, resinous materials having good impact
resistance are preferably used. Exemplary resins include polyester
elastomers, ionomer resins, styrene elastomers, hydrogenated
butadiene rubber and mixtures thereof. Use may be made of
commercially available polyester elastomers such as Hytrel 3078,
4047, and 4767 from Toray Dupont K.K.
[0034] Using a suitable mold, the intermediate layer may be formed
around the core by injection molding or compression molding. The
intermediate layer preferably has a thickness of 1.0 to 6.0 mm,
especially 2.0 to 5.0 mm.
[0035] In the other embodiment of the invention wherein protrusions
4a extend inward from the cover 4 into the intermediate layer 3 as
shown in FIG. 2, the intermediate layer at its outer surface is
provided with a plurality of recesses, preferably at the same time
as its molding. Specifically, the cavity of a mold for forming the
intermediate layer is formed on its inner surface with a plurality
of protrusions corresponding to the plurality of recesses. This
mold enables that the intermediate layer having a plurality of
recesses in its outer surface be formed by conventional injection
molding. In some cases, after a smooth intermediate layer is formed
around the core, recesses can be formed in the intermediate layer
by engraving, drilling or any other means.
[0036] The cover material is then molded around the intermediate
layer having a plurality of recesses in its outer surface by
conventional injection or compression molding, whereby the cover
having protrusions embedded in the intermediate layer is
formed.
[0037] Any of well-known cover stocks may be used in forming the
cover 3. The cover material may be selected from ionomer resins,
polyurethane resins, polyester resins and balata rubber. Use may be
made of commercially available ionomer resins such as Surlyn (du
Pont) and Himilan (Mitsui Dupont Polychemical K.K.
[0038] Additives such as titanium dioxide and barium sulfate may be
added to the cover stock for adjusting the specific gravity and
other properties thereof. Other optional additives include UV
absorbers, antioxidants, and dispersants such as metal soaps. The
cover may have a single layer structure of one material or be
formed to a multilayer structure from layers of different
materials.
[0039] The cover excluding the protrusions preferably has a
thickness of 0.5 to 4.0 mm, more preferably 1.0 to 2.5 mm. The
cover resin preferably has a Shore D hardness of 40 to 70, more
preferably 50 to 65.
[0040] The thus obtained golf ball has a multiplicity of dimples in
its surface. The ball on its surface is subject to finishing
treatments such as painting and stamping, if necessary. The golf
ball as a whole preferably has a hardness corresponding to a
deflection of 2.6 to 4.0 mm, more preferably 2.8 to 3.8 mm, under a
load of 100 kg. The golf ball must have a diameter of not less than
42.67 mm and a weight of not greater than 45.93 grams in accordance
with the Rules of Golf.
[0041] Since the protrusions extending from the core or cover are
embedded in the intermediate layer, made of a harder material than
the material of the intermediate layer, and satisfy the applicable
range of Euler's buckling formula, the golf ball of the invention
has the following benefits. When hit at a relatively high head
speed as with a driver, the ball is substantially deformed by
virtue of the buckling of the protrusions thereby accomplishing a
reduced backspin rate, an increased launch angle and an increased
carry. When the ball is struck at a relatively low head speed,
typically with a short iron, the protrusions does not buckle and
the ball undergoes small deformation, which provides an increased
backspin rate and maintains ease of control. With respect to the
"feel" of the ball when hit, the ball gives a feel in proportion to
the amount of deformation, that is, a soft pleasant feel on driver
shots.
EXAMPLE
[0042] Examples of the invention are given below by way of
illustration and not by way of limitation.
Examples 1-5 & Comparative Examples 1-5
[0043] Solid cores A to F were formed by working rubber
compositions of the formulation shown in Table 1 in a kneader and
molding and vulcanizing them in molds at a temperature of
155.degree. C. for about 15 minutes. Intermediate layers were
formed around the cores by injection molding resin compositions of
the formulation shown in Table 2. The combination of core and
intermediate layer is shown in Table 3. Covers were formed around
the intermediate layers by injection molding cover stocks of the
formulation shown in Table 2. The combination of cover with other
components is shown in Table 3. There were obtained three-piece
golf balls of Examples 1-5 and Comparative Examples 1-5.
[0044] The intermediate layer-forming molds used in Examples 1-5
and Comparative Examples 3-5 had cylindrical protrusions
distributed on their cavity-defining inner surface in a regular
octahedral arrangement. At the same time as molding of the
intermediate layer, it was formed with a plurality of recesses in
its surface. The cover material penetrated into the recesses
whereby the protrusions from the cover were embedded in the
intermediate layer. The number, cross-sectional shape,
cross-section size (diameter) and length of the protrusions are
reported in Table 3. In the balls of Examples 1-5, the protrusions
satisfied the applicable range of Euler's buckling formula, as seen
from the protrusion coefficient.
[0045] These golf balls were examined for hardness, flight
performance and feel by the following tests. The results are shown
in Table 4.
Ball Hardness
[0046] Hardness is expressed by a deflection (mm) under a load of
100 kg.
Flight Performance
[0047] Using a swing robot, the golf ball was struck with different
clubs at different head speeds (HS). A spin rate, initial velocity,
carry, and roll were measured.
[0048] (1) driver (W#1), HS 45 m/s
[0049] (2) driver (W#1), HS 35 m/s
[0050] (3) No. 5 iron (I#5), HS 39 m/s
[0051] (4) No. 9 iron (I#9), HS 35 m/s
[0052] The driver club used was Tour Stage X100 with a loft angle
of 10.degree., and the iron club was Tour Stage X1000, both
available from Bridgestone Sports Co., Ltd.
Feel
[0053] The balls were hit by three professional golfers using a
driver and pitching wedge. The feel of the balls upon impact was
rated by the golfers according to the following criteria.
[0054] Exc.: excellent feel
[0055] Good: good feel
[0056] Fair: ordinary feel
[0057] Poor: unpleasant feel
2TABLE 1 Core Rubber compound (pbw) A B C D E F JSR BR01*.sup.1
100.0 100.0 100.0 100.0 100.0 100.0 Zinc acrylate 20.0 20.0 25.0
25.0 25.0 25.0 Zinc oxide 10.0 10.0 10.0 10.0 10.0 10.0 Barium
sulfate 10.2 17.4 10.1 6.7 14.5 7.5 Dicumyl peroxide 1.2 1.2 1.2
1.2 1.2 1.2 *.sup.1polybutadiene rubber by Nippon Synthetic Rubber
K.K.
[0058]
3TABLE 2 Intermediate layer/Cover Resin blend (pbw) 1 2 3 4 5
Hytrel 3078*.sup.2 100.0 -- -- -- -- Hytrel 4047*.sup.2 -- 100.0 --
-- -- Hytrel 4767*.sup.2 -- -- 100.0 -- -- Himilan 1605*.sup.3 --
-- -- 50.0 -- Himilan 1650*.sup.3 -- -- -- -- 40.0 Himilan
1706*.sup.3 -- -- -- 50.0 -- Surlyn 8120*.sup.4 -- -- -- -- 60.0
Titanium oxide -- -- -- 5.0 5.0 *.sup.2polyester base thermoplastic
elastomer by Toray Dupont K.K. *.sup.3ionomer resin by Mitsui
Dupont Polychemical K.K. *.sup.4ionomer resin by E. I. duPont
[0059]
4TABLE 3 Example Comparative Example 1 2 3 4 5 1 2 3 4 5 Core
Compound A B C D E B C F B C Diameter (mm) 36.3 30.5 35.3 32.3 28.3
30.5 35.3 35.3 30.5 35.3 Weight (g) 28.4 17.5 26.4 19.9 13.9 17.5
26.4 26.1 17.5 26.4 Specific gravity 1.134 1.176 1.147 1.127 1.172
1.176 1.147 1.132 1.176 1.147 Hardness (mm)*.sup.5 4.1 3.9 3.5 3.3
3.4 3.9 3.5 3.5 3.9 4.0 Inter- Blend 3 1 2 1 2 1 2 3 1 2 mediate
Diameter (mm)*.sup.6 40.3 38.5 40.3 40.3 40.3 38.5 40.3 40.3 38.5
40.3 layer Thickness (mm) 2.0 4.0 2.5 4.0 6.0 4.0 2.5 2.5 4.0 2.5
Weight (g)*.sup.6 39.0 34.7 39.0 39.0 39.0 34.7 39.0 39.0 34.7 39.0
Specific gravity 1.15 1.15 1.12 1.15 1.12 1.15 1.12 1.15 1.15 1.12
Hardness (mm) 3.7 3.9 3.3 3.4 3.3 3.9 3.3 3.3 3.8 3.7 Hardness
(Shore D) 47 30 40 30 40 30 40 47 30 40 Cover Blend 4 4 5 5 5 4 5 5
4 5 Thickness (mm) 1.2 2.1 1.2 1.2 1.2 2.1 1.2 1.2 2.1 1.2 Weight
(g) 6.3 10.6 6.3 6.3 6.3 10.6 6.3 6.3 10.6 6.3 Specific gravity
0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 Hardness (Shore
D) 62 62 52 52 52 62 52 52 62 52 Young's modulus 270 270 90 90 90
270 90 90 270 90 (MPa) Yield stress 14.9 14.9 10.4 10.4 10.4 14.9
10.4 10.4 14.9 10.4 (MPa) Protrusions Number 344 152 344 152 120
nil nil 344 152 344 Cross-section circular circular circular
circular circular circular circular circular shape Cross-section
0.5 1.0 1.0 1.5 2.5 1.0 4.0 4.0 size (mm) Length (mm) 2.0 4.0 2.5
4.0 6.0 2.5 4.0 2.5 Protrusion 1.7 3.3 2.3 3.5 5.8 2.3 13.4 9.2
coefficient*.sup.7 *.sup.5deflection (mm) under a load of 100 kg
*.sup.6value for core and intermediate layer combined
*.sup.7.pi.(EI/A.sigma..sub.b).sup.1/2 wherein E is the Young's
modulus (MPa) of the cover material, I is the geometrical moment of
inertia (mm.sup.4) of the protrusion, A is the cross-sectional area
(mm.sup.2) of the protrusion, and .sigma..sub.b is the yield stress
(MPa) of the cover material.
[0060]
5TABLE 4 Example Comparative Example 1 2 3 4 5 1 2 3 4 5 Ball
Diameter (mm) 42.7 42.7 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 45.3 45.3
Hardness (mm) 3.0 3.1 3.2 3.5 3.2 3.1 3.2 3.1 3.0 3.6 W#1/HS45 Spin
(rpm) 2920 2760 2790 2760 2690 2930 3140 3080 2890 3070 Carry (m)
215.3 214.9 215.7 214.6 213.1 212.9 209.0 212.4 213.7 210.1 Total
(m) 220.6 223.5 223.2 222.4 219.8 218.7 215.8 217.6 219.4 216.5
Initial 68.0 68.1 68.1 68.0 67.9 68.0 67.9 68.0 68.1 67.9 velocity
(m/s) W#1/H535 Spin (rpm) 4360 4130 4160 4100 4010 4360 4690 4600
4140 4590 Carry (m) 142.7 141.2 141.5 140.8 139.7 139.7 137.1 139.0
140.9 138.3 Total (m) 158.4 160.4 160.2 159.1 157.2 156.0 154.3
155.8 155.7 154.9 I#5/HS39 Spin (rpm) 6590 6270 6230 6200 6150 5900
6120 6030 5720 6060 Carry (m) 153.9 155.3 155.1 154.8 154.7 156.8
154.1 155.1 155.1 155.7 Total (m) 156.9 159.7 159.0 159.2 158.9
163.5 159.8 160.0 162.8 161.2 Roll (m) 3.0 4.4 3.9 4.4 4.2 6.7 5.7
4.9 7.7 5.5 I#9/HS35 Spin (rpm) 9570 9210 9090 9070 9030 8200 8900
8750 8070 8560 Carry (m) 124.0 125.2 124.9 125.0 124.7 125.4 124.2
125.0 127.3 126.2 Total (m) 125.2 127.2 127.1 126.9 126.4 131.5
127.5 127.4 133.5 130.7 Roll (m) 1.2 2.0 2.2 1.9 1.7 6.1 3.3 2.4
6.2 4.5 Feel Driver Exc. Good Exc. Good Fair Fair Good Good Fair
Good Pitching wedge Exc. Exc. Exc. Exc. Good Poor Poor Poor Poor
Poor
[0061] Japanese Patent Application No. 125267/1998 is incorporated
herein by reference.
[0062] 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.
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