U.S. patent application number 09/294401 was filed with the patent office on 2001-09-27 for low drag and weight golf ball.
Invention is credited to AOYAMA, STEVEN, BOEHM, HERBERT C., MORGAN, WILLIAM E..
Application Number | 20010024983 09/294401 |
Document ID | / |
Family ID | 23133250 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010024983 |
Kind Code |
A1 |
MORGAN, WILLIAM E. ; et
al. |
September 27, 2001 |
LOW DRAG AND WEIGHT GOLF BALL
Abstract
A golf ball that has a core and a cover surrounding the core.
The cover has an exterior surface which defines a plurality of
dimples dimensioned and arranged such that the golf ball has a
coefficient of drag below about 0.26 at a Reynolds number of about
150,000 and a spin rate of about 3000 rpm. The cover and the core
are made from materials selected such that the golf ball has a
weight of below about 1.60 oz.
Inventors: |
MORGAN, WILLIAM E.;
(BARRINGTON, RI) ; BOEHM, HERBERT C.; (NORWELL,
MA) ; AOYAMA, STEVEN; (MARION, MA) |
Correspondence
Address: |
PENNIE & EDMONDS
1667 K STREE N W
WASHINGTON
DC
20006
|
Family ID: |
23133250 |
Appl. No.: |
09/294401 |
Filed: |
April 20, 1999 |
Current U.S.
Class: |
473/384 ;
473/378 |
Current CPC
Class: |
A63B 37/0003 20130101;
A63B 37/0083 20130101; A63B 37/002 20130101; A63B 37/0034 20130101;
A63B 37/0096 20130101; A63B 37/0065 20130101; A63B 37/00065
20200801; A63B 37/0089 20130101; A63B 37/0004 20130101; A63B
37/0064 20130101 |
Class at
Publication: |
473/384 ;
473/378 |
International
Class: |
A63B 037/00; A63B
037/12 |
Claims
What is claimed:
1. A golf ball comprising: (a) a core; and (b) a cover surrounding
the core and having an exterior surface defining a plurality of
dimples dimensioned and arranged such that the golf ball has a
coefficient of drag below about 0.26 at a Reynolds number of about
150,000 and a spin rate of about 3000 rpm; wherein the cover and
the core are made from materials selected such that the golf ball
has a weight of below about 1.60 oz.
2. The golf ball of claim 1, wherein the weight of the ball is
between about 1.5 and 1.6 oz.
3. The golf ball of claim 2, wherein the weight of the ball is
about 1.55 oz.
4. The golf ball of claim 1, wherein the materials of the core and
the cover are selected and configured such that the ball launches
at a spin rate of less than about 3000 rpm when struck under the
conditions set forth in the Overall Distance Standard for golf
balls established by the United States Golf Association.
5. The golf ball of claim 4, wherein the materials of the core and
the cover are selected and configured such that the ball launches
at a spin rate of less than about 2800 rpm when struck under the
conditions set forth in the Overall Distance Standard for golf
balls established by the United States Golf Association.
6. The golf ball of claim 4, wherein: (a) the core has a
compression of below about 90 points; and (b) the cover has a
hardness of greater than about 60 shore D.
7. The golf ball of claim 6, wherein the core comprises
polybutadiene and from about 1 to 10 parts by weight of calcium
oxide per hundred parts of polybutadiene.
8. The golf ball of claim 1, wherein the dimples are dimensioned
and arranged such that the golf ball has a coefficient of drag
below about 0.28 at a Reynolds number of about 130,000 and a spin
rate of about 3000 rpm.
9. The golf ball of claim 1, wherein the dimples are dimensioned
and arranged such that the golf ball has a coefficient of drag
below about 0.29 at a Reynolds number of about 120,000 and a spin
rate of about 3000 rpm.
10. The golf ball of claim 1, wherein the core includes a layer
including rubber windings.
11. A golf ball comprising: (a) a core; and (b) a cover surrounding
the core and having an exterior surface defining a plurality of
dimples which cover at least about 70% of the exterior surface and
which are configured such that the golf ball has a coefficient of
drag below about 0.26 at a Reynolds number of about 150,000 and a
spin rate of about 3000 rpm; wherein the core and the cover are
made from materials selected such that the golf ball has a weight
of below about 1.60 oz.
12. The golf ball of claim 11, wherein the exterior surface defines
at least about 440 of said dimples.
13. A golf ball comprising: (a) a core; and (b) a cover having an
exterior surface defining at least about 440 dimples which cover at
least about 70% of the exterior surface; wherein the core and the
cover are made from materials selected such that the golf ball has
a weight of below about 1.60 oz.
14. The golf ball of claim 13, wherein the exterior surface defines
at least about 550 of said dimples.
15. The golf ball of claim 14, wherein the exterior surface defines
less than about 700 of said dimples.
16. The golf ball of claim 14, wherein the exterior surface defines
about 650 of said dimples.
17. The golf ball of claim 13, wherein the dimples cover at least
about 80% of the exterior surface.
18. The golf ball of claim 13, wherein the dimples are arranged
such that up to one great circle path free from dimples is defined
on the exterior surface.
19. The golf ball of claim 13, wherein the dimples have an edge
angle of about 130 to a phantom sphere concentric with and having a
same diameter as the exterior surface of the cover.
Description
BACKGROUND OF THE INVENTION
[0001] Golf balls are typically constructed of a single or
multilayer core that is tightly surrounded by a single or
multilayer cover. It is typical for a golf ball core to be of solid
construction or wound construction. A solid core commonly comprises
polybutadiene, and a wound core typically comprises rubber threads
tightly wound around a solid or liquid center. The methods for
forming these cores are well known in the art. Traditionally, golf
ball covers are made of polymeric materials. For instance, covers
have been made of balata rubber, which may be natural balata,
synthetic balata or a blend of natural and synthetic balata, or
ionomers such as those sold under the trademark SURLYN.RTM..
[0002] The Rules of Golf as approved by the United States Golf
Association (USGA), includes the following rules that relate to
golf ball construction:
[0003] a. Weight
[0004] The weight of the ball shall not be greater than 1.620
ounces avoirdupois (45.92 gm).
[0005] b. Size
[0006] The diameter of the ball shall be not less than 1.680 inches
(42.67 mm). This specification will be satisfied if, under its own
weight, a ball falls through a 1.680 inches diameter ring gauge in
fewer than 25 out of 100 randomly selected positions, the test
being carried out at a temperature of 23+/-1.degree. C.
[0007] c. Spherical Symmetry
[0008] The ball must not be designed, manufactured or intentionally
modified to have properties which differ from those of a
spherically symmetrical ball.
[0009] d. Initial Velocity
[0010] The velocity of the ball shall not be greater than 250 feet
(76.2 m) per second when measured on apparatus approved by the
United States Golf Association. A maximum tolerance of 2% will be
allowed. The temperature of the ball when tested will be
23+/-1.degree. C.
[0011] e. Overall Distance Standard (ODS)
[0012] A brand of golf ball, when tested on apparatus approved by
the USGA on the outdoor range at the USGA Headquarters under the
conditions set forth in the Overall Distance Standard for golf
balls on file with the USGA, shall not cover an average distance in
carry and roll exceeding 280 yards (256 m) plus a tolerance of
6%.
[0013] The Initial Velocity rule test is well known. The test is
conducted by conditioning a ball for a minimum of 3 hrs at
23.+-.1.degree. C. The room in which the test is to be conducted is
conditioned to 23.+-.2.degree. C. The ball is then struck by a
striking mass of approximately 250 lbs at a striker velocity of
143.8 ft/sec.
[0014] The Overall Distance Standard test for golf balls is also
well known and is conducted by striking the golf ball with a golf
club having a lie of 55.+-.2, a D2.+-.1 swing weight,
11.+-.1.degree. loft angle, 13.3.+-.1 oz. overall weight,
4.6.+-.0.3 cycle per second vibrational frequency, 162.+-.30 oz.
in. moment of inertia, 43.5.+-.0.2 inches club length, a laminated
head construction, a cycolac insert, a stiff steel shaft, and an
all-weather rubber grip. The club head velocity during the ODS test
is about 160.+-.0.5 ft/sec measured at the hosel of the club over
the last 4 inches of travel prior to impact. The distance traveled
is adjusted for zero wind and an ambient temperature of 75.degree.
F. The setup of the specially designed mechanical-golfer apparatus
of the ODS test generally produces an initial ball velocity of
225-235 fps, a launch angle of 8.degree.-11.degree., and a spin
rate of 2300 to 3000 rpm using a known calibration ball.
[0015] The flight of a golf ball is determined by many factors, but
only three factors that are typically controlled by the golfer. By
impacting the ball with a golf club, the golfer typically controls
the speed of the golf ball, the launch angle, and the spin rate.
The launch angle sets the initial trajectory of the golf balls
flight. The speed and spin of the ball give the ball lift which
will define the balls overall flight path along with the weight and
drag of the golf ball. Where the ball stops after being struck by a
golf club also depends greatly on the weather and the landing
surface the ball contacts.
[0016] Many golfers have what is termed a "low swing-speed." This
means that the club head speed at impact is relatively slow when
compared to that of a professional golfer. Typically, an average
professional can drive a golf ball at a speed of approximately 235
fps (160 mph). A person having a low swing speed typically drives
the ball at a speed of less than 176 fps (120 mph). Most golfers
today have swing speeds that produce drives of less than 210 yards.
A person with a low swing speed generates a low ball speed. His or
her ball does not fly very far due to the lack of speed and
lift.
[0017] Low weight golf balls have been suggested in the past, such
as the Cayman Golf Company's SPECTRA.TM., the Ram LASER LIGHT.RTM.,
the Maxfli MD-80 and MD-90, and the Pinnacle EQUALIZER.RTM., which
weighs 1.55 oz. and has a hard core and a standard cover with 392
dimples. Low weight golf balls such as these have been made to
increase the lift to weight ratio of the golf ball, increasing the
effects of the lift on ball trajectory, and also to produce a
greater initial velocity upon impact than a heavier ball. It is
generally known that low weight golf balls slow down faster than
normal weight golf balls due to drag, an effect which is magnified
at higher speeds. As a result, low weight balls have been designed
to increase the lift to weight ratio, but not particularly to
decrease the effect of drag.
[0018] Attempts have been made in the past to minimize drag, but
these attempts have been focused only within a narrow window
optimized for higher swing-speed ball flight. Conventional dimple
patterns optimize lift to create the best trajectory for maximizing
distance. These conventional dimple designs, however, are
aerodynamically optimized for higher swing speeds than low
swing-speed players can achieve. Generally, as the lift of a dimple
pattern increases, drag also increases.
[0019] The advantages of a high spin, high lift golf ball are
minimized at the low air speeds achieved by a ball hit by low
swing-speed player. Since lift force increases with the square of
the ball speed, ball speed has a greater effect than ball spin in
creating lift, which produces a higher trajectory. When a player
strikes a ball, a portion of the energy from the club head is
transferred to the ball as ball speed, and another portion of the
energy is transferred to the ball as ball spin. Players with low
club swing speed necessarily will have less energy available to
transfer to both ball speed and ball spin. When club speed becomes
very low, the resulting ball speed can be low enough that the
effect of ball spin does not significantly increase lift force.
When the lift force exceeds the weight of the ball, the flight of
the ball is described as "aerodynamic." When the lift is less than
the weight of the ball, the ball flight is described as
"ballistic." Aerodynamic flight can generally be optimized by
balancing the relationship between ball speed, ball spin, and the
aerodynamic effect of the dimples. Ballistic flight can generally
be optimized by increasing the ball velocity, as a lift modifying
effect of the dimples is minimized. When compared to a ball hit by
a high swing-speed player, a similar ball that is hit by a low
swing-speed player travels along a more ballistic trajectory than
the aerodynamic trajectory achieved with a higher energy of a high
swing-speed player.
[0020] The dimples on a golf ball play an important part in
reducing drag and affecting lift. Drag is the air resistance that
acts on the golf ball in the opposite direction from the ball's
flight direction. As the spinning ball travels through the air, the
air surrounding the ball has different velocities and, thus,
different pressures. The air exerts maximum pressure at the
stagnation point on the front of the ball. The air then flows over
the sides of the ball and has increased velocity and reduced
pressure. At some point it separates from the surface of the ball,
leaving a large turbulent flow area behind the ball called the
wake, which has low pressure. The difference between the high
pressure in front of the ball and the low pressure behind the ball
slows the ball. This is the primary source of drag for a golf
ball.
[0021] The dimples on the ball create a turbulent boundary layer
around the ball, i.e., the air in a thin layer adjacent to the ball
flows in a turbulent manner. The turbulence energizes the boundary
layer and helps it remain attached further around the ball to
reduce the area of the wake. This greatly increases the average
pressure behind the ball and substantially reduces the drag.
[0022] Lift is the upward force on the ball that is created from a
difference in pressure between the top of the ball and the bottom
of the ball. The difference in pressure is created by a warpage in
the air flow resulting from the ball's back spin. Due to the back
spin, the top of the ball moves with the air flow, which delays the
separation to a point further aft. Conversely, the bottom of the
ball moves against the air flow, moving the separation point
forward. This asymmetrical separation creates an arch in the flow
pattern, requiring the air over the top of the ball to move faster,
and thus have lower pressure than the air underneath the ball.
[0023] Most golf ball manufacturers research dimple patterns in
order to increase the distance traveled by a golf ball. A high
degree of dimple coverage is beneficial to flight distance, but
dimple coverage gained by filling spaces between normally sized
dimples with tiny dimples is not very effective because tiny
dimples are not good turbulence generators. Most balls today have
many large spaces between dimples, or have filled these spaces with
very small dimples that do not create enough turbulence at average
golf ball velocities.
[0024] Low drag, low lift dimples are generally smaller than in
common golf balls and cover a large area of the surface of the golf
ball. Such dimples are taught, for example, in U.S. Pat. No.
4,560,168. This patent teaches a variety of dimple patterns for
golf balls. The dimple pattern is obtained by dividing the
spherical surface of the golf ball into twenty spherical triangles
corresponding to the faces of a regular icosahedron. Each of the
twenty triangles is further divided into four smaller triangles:
one central triangle and three apical triangles at the three apexes
of the larger triangle. This is done by connecting the midpoints of
the sides or edges of the larger triangle by great circle paths.
The dimples are arranged in each central triangle and each apical
triangle such so that no dimples intersect the edges of the central
triangle. The patent states that the size, numbering, and
configuration of the dimples should be selected to optimize
aerodynamic performance and minimize bald patches.
[0025] A golf ball with an improved ballistic, as opposed to
aerodynamic, trajectory is needed to improve play for low
swing-speed golfers.
SUMMARY OF THE INVENTION
[0026] The golf ball of the present invention provides improved
distance to golf players whose swing speed is too low to produce
sufficient lift to take advantage of aerodynamic flight. The ball
exhibits improved ballistic flight.
[0027] This improved flight is achieved by reducing the coefficient
of drag of the ball to below about 0.26 at a spin rate of 3000 rpm
and a Reynolds number of about 150,000, which corresponds to a ball
velocity of about 170 fps, and by reducing the weight of the ball
to below about 1.60 oz. Reducing the weight of the ball improves
initial velocity and distance at low launch velocities.
[0028] The dimple pattern selected for the golf ball is the primary
factor in reducing the coefficient of drag of the golf ball. The
golf ball of the present invention employs low-drag dimples, which
cover a large fraction of the exterior surface of the ball. The
preferred embodiments have dimples covering at least about 70% of
the exterior cover surface. Also, the number of dimples on the golf
ball surface is preferably large to minimize drag. Preferably, the
golf ball has at least about 440 dimples, and most preferably about
650.
[0029] Reducing spin on the ball also reduces the amount of energy
that becomes transferred to lifting the ball, and retains more
energy in translating the ball forward. The preferred golf ball
constructed according to the invention launches at a spin rate of
less than about 3000 rpm, which is considered a low spin rate, when
struck under the launch conditions set forth in the ODS test
established by the USGA.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a perspective view of a golf ball according to the
invention;
[0031] FIGS. 2 and 3 are detailed views of the dimple pattern of
the golf ball of FIG. 1;
[0032] FIGS. 4 and 5 are views of dimples on a golf ball;
[0033] FIG. 6 is a cross-sectional view of a golf ball according to
the invention;
[0034] FIG. 7 is a cross-sectional view of a dimple of the golf
ball of FIG. 6; and
[0035] FIGS. 8 and 9 are detailed views of an alternative dimple
pattern.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] Referring to FIGS. 1-3, solid lines 10 shown in FIG. 1 on
golf ball 12 form twenty icosahedral spherical triangles 14, which
correspond to faces of a regular icosahedron. The golf ball 12 has
a pattern of dimples 16 that is substantially repeated in each
icosahedral triangle 14. The icosahedron pattern has five triangles
14 formed at both the top and bottom of the ball 12. Each of the
five triangles 14 shares a vertex dimple 18. There are also ten
triangles 14 that extend around the middle of the ball 12.
[0037] FIGS. 2-3 provide the detailed layout of one of the
triangles 14 of FIG. 1. This dimple pattern has 642 dimples 16. The
pattern includes dimples 16 of sizes A and B formed in concentric
triangles 14, 20, and 22. Dimples B, disposed along the edges of
the icosahedral triangle 14, have a smaller diameter than dimples
A, which are disposed centrally within the icosahedral triangle 14,
along the edges of triangles 20 and 22.
[0038] Each of the edges of triangles 14 and 22 has an odd number
of dimples 16, and each of the edges of triangle 20 has an even
number of dimples 16. Each triangle 14 and 20 has nine more dimples
16 on its edges than its respective adjacent, smaller triangle 20
and 22. The large triangle 14 has a total of nine more dimples 16
on its edges than middle triangle 20, and middle triangle 20 has
nine more dimples 16 than small triangle 22.
[0039] This creates a hexagonal packing in which almost all dimples
16 are surrounded by six other dimples 16. Preferably at least 75%
of the dimples 16 have six adjacent dimples 16. More preferably,
only the vertex dimples do not have hexagonal packing.
[0040] For purposes of this application, as shown in FIG. 4, any
two dimples 16, such as dimples 16a and 16b, are considered
adjacent where four line segments 17, including two lines segments
17 drawn from a point tangent to each dimple 16a and 16b to the
center of the other dimple 16a and 16b, do not intersect any other
dimple 16. Dimples 16b and 16c, however, are not adjacent, as shown
in FIG. 5, as at least one of line segments 19, extending tangent
to one of the dimples 16b and 16c to the center of the other dimple
16b and 16c, intersects another dimple 16a or 16d. Also, dimples
with edges within about 0.03 inches of one another are also
considered adjacent. For simplicity, the examples of FIGS. 4 and 5
show the dimples lying on a flat surface, but it is understood that
dimples on a ball lie on a spherically curved surface, and line
segments 17 and 19 extend along great circle arcs.
[0041] Preferably, in the golf balls according to the present
invention, less than 30% of the spacings between adjacent dimples
16 are greater than 0.01 inches. More preferably, less than 15% of
the spacings between adjacent dimples 16 is greater than 0.01
inches.
[0042] In the golf ball shown in FIGS. 1-3, there is no great
circle path that is does not intersect any dimples 16. This
increases the percentage of the outer surface that is covered by
dimples 16. Golf balls according to the present invention
preferably have dimples 16 arranged so that there are less than
four great circle paths that do not intersect any dimples 16. There
is more preferably no great circle path, or only one great circle
path at the equator, that does not intersect any dimples 16.
[0043] Providing one equator that does not intersect any dimples 16
facilitates manufacturing, however, in particular the step of
buffing golf balls after molding. Also, many players prefer to have
an equator that they can use to line up putts. Thus, dimple
patterns often have modified triangles 14 around the mid-section to
create the equator that does not intersect any dimples 16.
[0044] FIG. 6 diagrammatically illustrates a cross-section of a
golf ball 24. Golf ball 24 has a pattern of dimples 16 formed on
the exterior surface of a cover 26. The cover 26 surrounds a core
28, and in the embodiment shown, the core 28 includes a mantle
layer 30 and a center 32, however, additional mantle layers or
cover layers may also be used. In a one piece alternative
embodiment, the cover 26 and the core 28 are made from a single
piece of material.
[0045] Referring to FIG. 7, each dimple 16 has a frustospherical
shape. The diameter 34 and depth 36, which is measured from the
deepest point of the dimple 16 to the perimeter of a phantom sphere
38 that has the diameter of the golf ball 24, can be plainly seen.
Dimples A of FIGS. 1-3 preferably have a diameter of about 0.12
inches, and dimples B preferably have a diameter of about 0.11
inches. In the preferred embodiment, there are 420 dimples A and
222 dimples B. Together, the dimples 16 cover about 77% of the golf
ball 12.
[0046] The walls of the dimple 16, where they meet the undimpled
portion of the exterior surface, are formed at an edge angle 40
tangential to this undimpled portion. Edge angle 40 is preferably
between about 10.degree. and 18.degree., and most preferably about
13.degree..
[0047] Since the depth 36 and diameter 34 of the dimples 16 can be
used to calculate the total dimple volume for a articular golf
ball, the low-drag dimples 16 of the present invention can also be
described by the total dimple volume they enclose between the
exterior surface of the cover 26 and the phantom sphere 38.
[0048] Referring to FIGS. 8-9, another suitable, low-drag dimple
pattern is formed on a golf ball divided into eight triangles on
the surface of the cover, in an octahedral pattern, with the
dimples 16 being inside the octahedral triangle 41 shown. This golf
ball dimple pattern embodiment has 440 dimples 16 of six different
sizes.
[0049] The dimples 16 are formed in large triangles 42, middle
triangles 44, and small triangles 46. In this embodiment, each of
the edges of the large triangle 42 has an even number of dimples
16, each of the edges of the middle triangle 44 has an odd number
of dimples 16, and each of the edges of the small triangle 42 has
an even number of dimples 16. The large triangle 42 has nine more
dimples 16 than the middle triangle 44, and the middle triangle 44
has nine more dimples 16 than the small triangle 46. This creates a
hexagonal packing for all of the dimples 16 inside the large
triangles 42, increasing dimple coverage of the exterior surface of
the ball.
[0050] In this embodiment, the diameters of the dimples of the
different sizes are as follow:
[0051]
1 Dimple A B C D E F Diameter (in.) .09 .11 .14 .15 .16 .17
[0052] The above dimple sizes render a surface coverage of about
82%.
[0053] The preferred low-drag dimple patterns in this invention
further have dimples 16 that cover at least about 70% of the
exterior surface of the ball, and more preferably at least about
80% of the exterior surface of the ball.
[0054] In golf balls constructed according to the invention, most
of the dimples 16 preferably have a diameter of up to about 0.15
inches. More preferably, at least about 70% of the dimples 16 have
a diameter of about 0.13 inches or less, and about 100% of the
dimples 16 have a diameter of about 0.15 inches or less.
[0055] In terms of drag coefficient, whereas at professional launch
speeds a golf ball with around 400 dimples produces the lowest
coefficient of drag, it has been found that at a spin rate of about
3000 rpm and a Reynolds number of about 150,000, which corresponds
to a launch speed of about 170 fps, the lowest drag coefficient is
achieved with a golf ball that has about 650 dimples. The
coefficient of drag achieved with this number of dimples is
slightly above 0.25. At even slower launch speeds, a higher number
of dimples is preferred. For example, at a Reynolds number of about
120,000, about 800 dimples provide the least drag.
[0056] As the golf balls of the invention are tailored to improve
the distance achieved by low swing-speed players, these golf balls
preferably have a coefficient of drag of less than about 0.26 at a
Reynolds number of 150,000 and a spin rate of 3000 rpm. Also, at a
Reynolds number of about 130,000, the golf balls preferably have a
drag coefficient of less than about 0.28, and more preferably of
less than 0.27. At a Reynolds number of 120,000, the golf balls
preferably have a coefficient of drag of less than about 0.29, and
more preferably less than about 0.28.
[0057] Preferably, the golf ball has at least about 440 dimples.
More preferably, the golf ball has above about 500 dimples, and
most preferably between about 550 and about 700 dimples. Golf balls
tailored to even lower swing speeds may have 800 dimples or
more.
[0058] Furthermore, the preferred embodiment has a low-spin
construction in order to minimize lift and the amount of energy
converted to lift instead of forward motion. The embodiments of
this invention may be of solid construction, as shown in FIG. 6;
wound construction, in which the mantle layer 30 can be replaced
with tightly wound rubber windings; or any other type of
construction known in the art. The cover 26 shown in FIG. 6 has a
single layer, but may include additional layers. Similarly, the
core 28 shown has two layers, but may instead include only a center
or multiple mantle layers.
[0059] A low spin-rate is achieved by providing a hard cover 26 and
a soft core 28. A wide variety of cover materials may be used in
the present invention. Among the preferred conventional cover
materials are ionomer resins. More particularly, blends of
ionomers, including acid-containing olefin copolymer ionomers, are
preferred. These ionomers are copolymers of an olefin such as
ethylene and an alpha, beta-unsaturated carboxylic acid such as
acrylic or methacrylic acid present in 5-35 (preferably 10-35, most
preferably 15-20) weight percent of the polymer, wherein the acid
moiety is neutralized 1%-90% (preferably at least 40%, most
preferably at least about 60%) to form an ionomer by a cation such
as lithium, sodium, potassium, magnesium, calcium, barium, lead,
tin, zinc or aluminum, or a combination of such cations, lithium,
sodium and zinc being the most preferred. Specific acid-containing
ethylene copolymers include ethylene/acrylic acid,
ethylene/methacrylic acid, ethylene/acrylic acid/n-butyl acrylate,
ethylene/methacrylic acid/n-butyl acrylate, ethylene/methacrylic
acid/iso-butyl acrylate, ethylene/acrylic acid/iso-butyl acrylate,
ethylene/methacrylic acid/n-butyl methacrylate, ethylene/acrylic
acid/methyl methacrylate, ethylene/acrylic acid/methyl acrylate,
ethylene/methacrylic acid/methyl acrylate, ethylene/methacrylic
acid/methyl methacrylate, and ethylene/acrylic acid/n-butyl
methacrylate. Preferred acid-containing ethylene copolymers include
ethylene/methacrylic acid, ethylene/acrylic acid,
ethylene/methacrylic acid/n-butyl acrylate, ethylene/acrylic
acid/n-butyl acrylate, ethylene/methacrylic acid/methyl acrylate
and ethylene/acrylic acid/methyl acrylate copolymers. The most
preferred acid-containing ethylene copolymers are
ethylene/methacrylic acid, ethylene/acrylic acid,
ethylene/(meth)acrylic acid/n-butyl acrylate,
ethylene/(meth)acrylic acid/ethyl acrylate, and
ethylene/(meth)acrylic acid/methyl acrylate copolymers.
[0060] The manner in which these ionomers are made is well known in
the art as described in U.S. Pat. No. 3,262,272, for example. A
preferred cover is comprised of a blend of ionomer resins that are
copolymers of 80% to 95% of an olefin such as ethylene and about
13%-16% by weight of an alpha, beta-unsaturated carboxylic acid,
wherein about 10%-90% of the carboxylic acid groups are neutralized
with a metal ion. Preferably, a first ionomer is neutralized with
lithium and a second ionomer is neutralized with sodium.
Preferably, the blend comprises between 10% and 65% of the lithium
ionomer and between 90% and 45% of the sodium ionomer. Most
preferably, the blend is a 50/50 blend. Suitable ionomers include
SURLYN.RTM. 8140, which is a sodium ionomer that has greater than
16% by weight of an alpha, delta-unsaturated carboxylic acid;
SURLYN.RTM. 9910, which is a zinc SURLYN.RTM. that has about 15% by
weight of an alpha, delta-unsaturated carboxylic acid; and
SURLYN.RTM. 7940, which is a standard lithium ionomer. Still
further, the preferred cover has a hardness of greater than about
60 shore D and a flexural modulus of between about 60 and 70 ksi.
The high flexural modulus of the cover 26 not only lowers the spin
rate, but also can provide increased initial velocity, further
benefitting a low swing-speed player. Other useful SURLYN.RTM.
ionomers include SURLYN.RTM. 8118 and SURLYN.RTM. 7930, which have
flexural moduli of about 61 ksi.
[0061] Soft cores produce low spin rates. The core 28 has a reduced
compression to slow the ball's spin and reduce lift and drag.
Preferably, the compression of the core 28 is below about 90
points. If the compression of the ball as a whole drops too far,
however, the initial velocity may decrease excessively.
[0062] As used herein, the terms "points" or "compression points"
refer to the standard compression scale based on the ATTI
Engineering Compression Tester. This scale, which is well known to
those working in this field, is used in determining the relative
compression of a core or ball and has been referred to as PGA
compression.
[0063] Zinc oxide (ZnO) in the core 28 may be reduced or eliminated
in favor of calcium oxide (CaO). Such a composition can maintain
the initial velocity of the ball near or even above the maximum
allowed by the USGA, while reducing the compression of the core 28
by at least about 2 compression points to as much as about 14
points. Where the amount of zinc oxide traditionally incorporated
in cores is typically about 5 to 50 pph of polybutadiene, the
amount of calcium oxide preferably added to the core-forming
composition of the invention as an activator is typically in the
range of about 0.1 to 15, and most preferably 1.25 to 5 pph. A
wound construction of the core may also be employed to increase the
initial velocity of the ball.
[0064] The construction of the golf ball is preferably selected
such that when the ball is struck squarely by a golf club head
moving at the speed of about 160 fps with a dynamic loft angle of
about 10.degree.-12.degree., the ball achieves a spin rate of less
than about 3000 rpm, which is considered a low spin rate. More
preferably, the spin rate achieved under these strike conditions is
between 2000 and 2800 rpm, and most preferably the ball achieves a
spin rate below about 2600 rpm. The spin rate is preferably above
2000 rpm, as spin rates much below 2000 rpm tend to produce
unstable airflow patterns, resulting in unpredictable ball flight.
As these strike conditions are used in the ODS test, these spin
rates can be described in terms of the spin achieved under ODS
strike conditions.
[0065] Golf balls according to the present invention have a weight
reduced from the normal. This increases the initial velocity of the
golf ball and further improves the distance covered by the ball
when struck by a low swing-speed player. Generally, fillers are
added to golf ball cores in order to control the weight of the ball
and bring the ball mass up to the maximum specified by the USGA.
Useful fillers include zinc oxide, barium sulfate, and regrind,
which is recycled core molding scrap ground to 30 mesh particle
size.
[0066] The preferred weight of golf balls according to the
invention is below about 1.60 oz, more preferably between about 1.5
oz. and 1.6 oz., and most preferably between about 1.55 oz. and
1.56 oz. It is preferred that a reduction in core mass be
accomplished by reducing the amount of fillers that are added when
compared to a USGA regulation ball. Also, any filler can be added
in a manner such that ball density increases with distance from the
geometric center of the golf ball to increase the rotational moment
of inertia of the golf ball to lower the spin of the ball when it
is hit.
[0067] Typical golf balls with solid polybutadiene cores 28 have a
specific gravity of about 1.25. Golf balls of the present invention
are preferably comprised of low weight polybutadiene with a
specific gravity of less than the standard 1.25.
[0068] In balls with liquid centers, a mixture of corn syrup, salt
and water may be employed as the liquid. Corn syrup and salt are
added to increase the specific gravity and viscosity. A low center
density is desirable, however, to minimize weight. Low-weight
liquid centers are preferred and may use water only or a Barium
Sulfate (BaSO.sub.4) paste.
[0069] It will be appreciated that numerous modifications to the
embodiments described above and other embodiments, such as golf
balls with tetrahedral dimple patterns, may be devised by those
skilled in the art. Therefore, the appended claims are intended to
cover all modifications and embodiments which come within the
spirit and scope of the present invention.
* * * * *