U.S. patent application number 11/637839 was filed with the patent office on 2008-06-19 for multi-piece solid golf ball.
This patent application is currently assigned to BRIDGESTONE SPORTS CO., LTD.. Invention is credited to Hideo Watanabe.
Application Number | 20080146377 11/637839 |
Document ID | / |
Family ID | 39528047 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080146377 |
Kind Code |
A1 |
Watanabe; Hideo |
June 19, 2008 |
Multi-piece solid golf ball
Abstract
The invention provides a multi-piece solid golf ball having a
core, an envelope layer encasing the core, an intermediate layer
encasing the envelope layer, and a cover which encases the
intermediate layer and has formed on a surface thereof a plurality
of dimples. The core is formed primarily of a rubber material and
has a diameter of at least 31 mm, the envelope layer and the
intermediate layer are each formed primarily of the same or
different resin materials, and the cover is formed primarily of
polyurethane. The intermediate layer and the cover have thicknesses
which satisfy the relationship: cover thickness<intermediate
layer thickness. The core has a surface hardness (Durometer D
hardness) and the envelope layer, intermediate layer and cover have
material hardnesses (Durometer D hardness) which together satisfy
the relationship: cover material hardness<intermediate layer
material hardness<envelope layer material hardness>core
surface hardness. The golf ball of the invention, as a ball for
professionals and skilled amateur golfers, has both an excellent
controllability and flight as well as an excellent feel on impact,
in addition to which it has a good scuff resistance, enabling it to
endure harsh conditions of use.
Inventors: |
Watanabe; Hideo;
(Chichibu-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
Tokyo
JP
|
Family ID: |
39528047 |
Appl. No.: |
11/637839 |
Filed: |
December 13, 2006 |
Current U.S.
Class: |
473/376 |
Current CPC
Class: |
A63B 37/0092 20130101;
A63B 37/0045 20130101; A63B 37/0033 20130101; A63B 37/0031
20130101 |
Class at
Publication: |
473/376 |
International
Class: |
A63B 37/06 20060101
A63B037/06 |
Claims
1. A multi-piece solid golf ball comprising a core, an envelope
layer encasing the core, an intermediate layer encasing the
envelope layer, and a cover which encases the intermediate layer
and has formed on a surface thereof a plurality of dimples, wherein
the core is formed primarily of a rubber material and has a
diameter of at least 31 mm, the envelope layer and the intermediate
layer are each formed primarily of the same or different resin
materials, and the cover is formed primarily of polyurethane; the
envelope layer, the intermediate layer and the cover have
thicknesses which satisfy the relationship: cover
thickness<intermediate layer thickness<envelope layer
thickness; and the core has a surface hardness (Durometer D
hardness) and the envelope layer, intermediate layer and cover have
material hardnesses (Durometer D hardness) which together satisfy
the relationship; cover material hardness<intermediate layer
material hardness<envelope layer material hardness<core
surface hardness.
2. (canceled)
3. The multi-piece solid golf ball of claim 1, wherein the resin
material which forms the envelope layer comprises an ionomer resin
having an acid content of at least 16 wt %.
4. The multi-piece solid golf ball of claim 1, wherein the resin
material which forms the cover is composed primarily of: (A) a
thermoplastic polyurethane material, and (B) an isocyanate mixture
obtained by dispersing (b-1) a compound having two or more
isocyanate groups as functional groups per molecule in (b-2) a
thermoplastic resin which is substantially non-reactive with
isocyanate.
5. The multi-piece solid golf ball of claim 1, wherein the envelope
layer, intermediate layer and cover have material hardnesses
(Durometer D hardnesses) such that 60.ltoreq.envelope layer
material hardness.ltoreq.70, 55.ltoreq.intermediate layer material
hardness.ltoreq.70, and 30.ltoreq.cover material
hardness.ltoreq.55.
6. The multi-piece solid golf ball of claim 1, wherein the ball and
the core have deflections (mm), when compressed under a final load
of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf), which
satisfy the following respective conditions: 2.0 mm.ltoreq.ball
deflection.ltoreq.3.0 mm, and 3.5 mm.ltoreq.core
deflection.ltoreq.6.0 mm.
7. The multi-piece solid golf ball of claim 1, wherein the core
surface hardness is lower than the material hardness of the
envelope layer by a difference in Durometer D hardness of 5 to
35.
8. The multi-piece solid golf ball of claim 1, wherein the
difference between the hardness of the envelope layer material and
the hardness of the intermediate layer material is at least 1 but
not more than 20 in Durometer D hardness.
9. The multi-piece solid golf ball of claim 1, wherein the surface
of the intermediate layer is abraded.
10. The multi-piece solid golf ball of claim 9, wherein a primer is
applied to the surface of the intermediate layer after the
abrasion.
11. The multi-piece solid golf ball of claim 9, wherein an adhesion
reinforcing agent is added to the intermediate layer material after
the abrasion.
12. The multi-piece solid golf ball of claim 11, wherein the
adhesion reinforcing agent is selected from the group consisting of
1,3-butanediol, trimethylolpropane, polyethylene glycol oligomer
and polyhydroxy polyolefin oligomer.
13. The multi-piece solid golf ball of claim 1, wherein the numbers
of the dimples arranged on the cover surface is at least 280 but
not more than 360.
14. The multi-piece solid golf ball of claim 1, wherein the
diameter of the dimples is set to at least about 2.5 mm but not
more than about 6.5 mm.
15. The multi-piece solid golf ball of claim 1, wherein the dimple
coverage on the spherical surface of the golf ball, which is the
sum of the individual dimple surface areas, each defined by the
border of the flat plane circumscribed by the edge of the dimple,
expressed as a ratio (SR) with respect to the spherical surface
area of the ball were it to be free of dimples, is at least 60% but
not more than 90%.
16. The multi-piece solid golf ball of claim 1, wherein the value
V.sub.0 obtained by dividing the spatial volume of each dimple
below the flat plane circumscribed by the edge of that dimple by
the volume of a cylinder whose base is the flat plane and whose
height from the base to the maximum depth of the dimple is at least
0.35 but not more than 0.80.
17. The multi-piece solid golf ball of claim 1, wherein the VR
value, which is the sum of the volumes of individual dimples formed
below flat planes circumscribed by the dimple edges, as a
percentage of the volume of the ball sphere were it to have no
dimples thereon, is at least 0.6% but not more than 1.0%.
18. The multi-piece solid golf ball of claim 1, wherein the ball
has deflection of 2.0 to 2.2 mm, when compressed under a final load
of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf).
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a multi-piece solid golf
ball composed of a core, an envelope layer, an intermediate layer
and a cover that have been formed as successive layers. More
specifically, the invention relates to a multi-piece solid golf
ball which has a flight performance and controllability that
satisfy the needs of professionals and other skilled golfers, and
which also has a good feel on impact and an excellent scuff
resistance.
[0002] A variety of golf balls have hitherto been developed for
professionals and other skilled golfers. Of these, multi-piece
solid golf balls having an optimized hardness relationship between
an intermediate layer encasing the core and the cover layer are in
wide use because they achieve both a superior distance in the high
head speed range and good controllability on shots taken with an
iron and on approach shots. Another important concern is the proper
selection of thicknesses and hardnesses for the respective layers
of the golf ball so as to optimize not only flight performance, but
also both the feel of the ball when played as well as its spin rate
after being struck with the club, particularly given the large
influence these latter factors have on ball control. A further key
concern in ball development, arising from the desire that golf
balls also have durability under repeated impact and scuff
resistance against burr formation on the surface of the ball when
repeatedly played with different types of clubs, is how best to
protect the ball from external factors.
[0003] The three-piece solid golf balls having an outer layer cover
formed primarily of a thermoplastic polyurethane which are
disclosed in, for example, JP-A 2003-190330, JP-A 2004-049913, JP-A
2004-97802 and JP-A 2005-319287 were intended to meet such needs.
However, because these prior-art golf balls fail to achieve a
sufficiently lower spin rate when hit with a driver, professionals
and other skilled golfers have desired a ball which delivers an
even longer distance.
[0004] Meanwhile, efforts to improve the flight and other
performance characteristics of golf balls have led to the
development of balls having a four-layer construction--i.e., a core
enclosed by three intermediate or cover layers--that allows the
ball construction to be varied among the several layers at the
interior. Such golf balls have been disclosed in, for example, JP-A
2004-180822, JP-A 10-127818, JP-A 10-127819, JP-A 10-295852, U.S.
Pat. No. 5,816,937, U.S. Pat. No. 6,152,834, U.S. Pat. No.
6,123,630, U.S. Pat. No. 6,468,169, U.S. Pat. No. 6,045,460, U.S.
Pat. No. 6,248,027, U.S. Pat. No. 6,117,026 and U.S. Pat. No.
6,277,036.
[0005] Yet, as golf balls for the skilled golfer, such balls
provide a poor balance of distance and controllability or they fall
short in terms of achieving a lower spin rate on shots with a
driver, thus limiting the extent to which the total distance can be
increased.
SUMMARY OF THE INVENTION
[0006] It is therefore an object of the present invention to
provide a multi-piece solid golf ball which has a flight
performance and controllability that are fully acceptable to
professionals and other skilled golfers, while also having an
excellent durability to cracking on repeated impact and an
excellent scuff resistance.
[0007] In the present invention, the golf ball design consists
basically of an outermost layer made of polyurethane and a
multilayer structure of three or more outer layers (envelope
layer/intermediate layer/cover) encasing the core. By making the
cover, or outermost layer, of polyurethane, which is relatively
soft, a spin performance on approach shots that is acceptable to
professionals and other skilled golfers and a high scuff resistance
are obtained. By forming the envelope layer of a material which is
harder than the core surface and the intermediate layer, the spin
rate of the ball on shots with a driver (W#1) can be lowered. In
addition, by imparting to the respective layers in the
core/envelope layer/intermediate layer/cover construction the
following hardness relationship: cover material
hardness<intermediate layer material hardness<envelope layer
material hardness>core surface hardness, and by optimizing the
core diameter and the relationship between the intermediate layer
and the cover layer thicknesses, it was possible through the
synergistic effects of these hardness relationships and layer
thickness relationships to resolve the above-described problems
encountered in the prior art. That is, the golf ball of the
invention, when used by professionals and other skilled golfers,
provides a fully acceptable flight performance and controllability,
in addition to which it exhibits an excellent durability to
cracking on repeated impact and excellent scuff resistance, effects
which were entirely unanticipated. Having thus found that the
technical challenges recited above can be overcome by the foregoing
arrangement, the inventors ultimately arrived at the present
invention.
[0008] Accordingly, the invention provides the following
multi-piece solid golf balls. [0009] [1] A multi-piece solid golf
ball comprising a core, an envelope layer encasing the core, an
intermediate layer encasing the envelope layer, and a cover which
encases the intermediate layer and has formed on a surface thereof
a plurality of dimples, wherein the core is formed primarily of a
rubber material and has a diameter of at least 31 mm, the envelope
layer and the intermediate layer are each formed primarily of the
same or different resin materials, and the cover is formed
primarily of polyurethane; the intermediate layer and the cover
have thicknesses which satisfy the relationship: cover
thickness<intermediate layer thickness; and the core has a
surface hardness (Durometer D hardness) and the envelope layer,
intermediate layer and cover have material hardnesses (Durometer D
hardness) which together satisfy the relationship: cover material
hardness<intermediate layer material hardness<envelope layer
material hardness>core surface hardness. [0010] [2] The
multi-piece solid golf ball of [1], wherein the thicknesses of the
envelope layer, the intermediate layer and the cover satisfy the
relationship: cover thickness<intermediate layer
thickness<envelope layer thickness. [0011] [3] The multi-piece
solid golf ball of [1], wherein the resin material which forms the
envelope layer comprises an ionomer resin having an acid content of
at least 16 wt %. [0012] [4] The multi-piece solid golf ball of
[1], wherein the resin material which forms the cover is composed
primarily of (A) a thermoplastic polyurethane material, and (B) an
isocyanate mixture obtained by dispersing (b-1) a compound having
two or more isocyanate groups as functional groups per molecule in
(b-2) a thermoplastic resin which is substantially non-reactive
with isocyanate. [0013] [5] The multi-piece solid golf ball of [1],
wherein the envelope layer, intermediate layer and cover have
material hardnesses (Durometer D hardnesses) such that:
60.ltoreq.envelope layer material hardness.ltoreq.70,
55.ltoreq.intermediate layer material hardness.ltoreq.70, and
30.ltoreq.cover material hardness.ltoreq.55. [0014] [6] The
multi-piece solid golf ball of [1], wherein the ball and the core
have deflections (mm), when compressed under a final load of 1,275
N (130 kgf) from an initial load of 98 N (10 kgf), which satisfy
the following respective conditions: 2.0 mm.ltoreq.ball
deflection.ltoreq.3.0 mm, and 3.5 mm.ltoreq.core
deflection.ltoreq.6.0 mm.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0015] FIG. 1 is a schematic sectional view showing a multi-piece
solid golf ball (4-layer construction) according to the
invention.
[0016] FIG. 2 is a top view of a golf ball showing the arrangement
of dimples used in the examples of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The invention is described more fully below. The multi-piece
solid golf ball of the present invention, as shown in FIG. 1, is a
golf ball G having four or more layers, including a core 1, an
envelope layer 2 which encases the core, an intermediate layer 3
which encases the envelope layer, and a cover 4 which encases the
intermediate layer. The cover 4 typically has a large number of
dimples D formed on the surface thereof. The core 1 and the
intermediate layer 3 are not limited to single layers, and may each
be formed of a plurality of two more layers.
[0018] In the invention, the core diameter is set to at least 31
mm, and is generally at least 31 mm but not more than 38 mm,
preferably at least 32.5 mm but not more than 37 mm, and more
preferably at least 34 mm but not more than 36 mm. A core diameter
outside this range will lower the initial velocity of the ball or
yield a less than adequate spin rate-lowering effect after the ball
is hit, as a result of which an increased distance may not be
achieved.
[0019] The surface hardness of the core, while not subject to any
particular limitation, preferably has a Durometer D hardness (the
value measured with a type D durometer based on ASTM D2240; the
same applies to the hardnesses described below for the respective
layers) of generally at least 35 but not more than 60, more
preferably at least 40 but not more than 55, and even more
preferably at least 43 but not more than 50. Below the above range,
the ball may have an inadequate rebound and thus fail to achieve
the desired distance, and the durability to cracking on repeated
impact may worsen. Conversely, at a core surface hardness higher
than the above range, the ball may have an excessively hard feel on
full shots with a driver and the spin rate may be too high, as a
result of which the desired distance may not be achieved.
[0020] The deflection when the core is compressed under a final
load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf),
while not subject to any particular limitation, is preferably set
within a range of at least 3.5 mm but not more than 6.0 mm, more
preferably at least 3.8 mm but not more than 5.6 mm, and even more
preferably at least 4.2 mm but not more than 5.2 mm. If this value
is too low, the core may lack sufficient rebound, which may result
in a less than adequate distance, and the durability of the ball to
cracking on repeated impact may worsen. On the other hand, if this
value is too high, the ball may have an excessively hard feel on
full shots with a driver, and the spin rate may be too high, as a
result of which an increased distance may not be achieved.
[0021] The core surface hardness must be lower than the material
hardness of the envelope layer. The difference between the hardness
of the envelope layer material and the core surface hardness is
generally from 5 to 35, preferably from 10 to 30, and more
preferably from 15 to 25. Outside of this range, the ball as a
whole will have an inappropriate hardness and a poor feel.
Moreover, the rebound will be insufficient or the spin
rate-lowering effect will be inadequate, which may prevent the
desired distance from being achieved.
[0022] The solid core may be formed of a rubber composition
containing, for example, a co-crosslinking agent, an organic
peroxide, an inert filler and an organosulfur compound. It is
preferable to use polybutadiene as the base rubber of the rubber
composition.
[0023] It is desirable for the polybutadiene serving as the rubber
component to have a cis-1,4-bond content on the polymer chain of at
least 60 wt %, preferably at least 80 wt %, more preferably at
least 90 wt %, and most preferably at least 95 wt %. Too low a
cis-1,4-bond content among the bonds on the molecule may lead to a
lower resilience.
[0024] Moreover, the polybutadiene has a 1,2-vinyl bond content on
the polymer chain of typically not more than 2%, preferably not
more than 1.7%, and even more preferably not more than 1.5%. Too
high a 1,2-vinyl bond content may lead to a lower resilience.
[0025] To obtain a molded and vulcanized rubber composition of good
resilience, the polybutadiene used in the invention is preferably
one synthesized with a rare-earth catalyst or a Group VIII metal
compound catalyst. Polybutadiene synthesized with a rare-earth
catalyst is especially preferred.
[0026] Such rare-earth catalysts are not subject to any particular
limitation. Exemplary rare-earth catalysts include those made up of
a combination of a lanthanide series rare-earth compound with an
organoaluminum compound, an alumoxane, a halogen-bearing compound
and an optional Lewis base.
[0027] Examples of suitable lanthanide series rare-earth compounds
include halides, carboxylates, alcoholates, thioalcoholates and
amides of atomic number 57 to 71 metals.
[0028] In the practice of the invention, the use of a neodymium
catalyst in which a neodymium compound serves as the lanthanide
series rare-earth compound is particularly advantageous because it
enables a polybutadiene rubber having a high cis-1,4 bond content
and a low 1,2-vinyl bond content to be obtained at an excellent
polymerization activity. Suitable examples of such rare-earth
catalysts include those mentioned in JP-A 11-35633, JP-A 11-164912
and JP-A 2002-293996.
[0029] To enhance the resilience, it is preferable for the
polybutadiene synthesized using the lanthanide series rare-earth
compound catalyst to account for at least 10 wt %, preferably at
least 20 wt %, and more preferably at least 40 wt %, of the rubber
components.
[0030] Rubber components other than the above-described
polybutadiene may be included in the base rubber insofar as the
objects of the invention are attainable. Illustrative examples of
rubber components other than the above-described polybutadiene
include other polybutadienes, and other diene rubbers, such as
styrene-butadiene rubber, natural rubber, isoprene rubber and
ethylene-propylene-diene rubber.
[0031] Examples of co-crosslinking agents include unsaturated
carboxylic acids and the metal salts of unsaturated carboxylic
acids.
[0032] Specific examples of unsaturated carboxylic acids include
acrylic acid, methacrylic acid, maleic acid and fumaric acid.
Acrylic acid and methacrylic acid are especially preferred.
[0033] The metal salts of unsaturated carboxylic acids, while not
subject to any particular limitation, are exemplified by the
above-mentioned unsaturated carboxylic acids neutralized with a
desired metal ion. Specific examples include the zinc and magnesium
salts of methacrylic acid and acrylic acid. The use of zinc
acrylate is especially preferred.
[0034] The unsaturated carboxylic acid and/or metal salt thereof is
included in an amount, per 100 parts by weight of the base rubber,
of generally at least 10 parts by weight, preferably at least 15
parts by weight, and more preferably at least 20 parts by weight,
but generally not more than 60 parts by weight, preferably not more
than 50 parts by weight, more preferably not more than 45 parts by
weight, and most preferably not more than 40 parts by weight. Too
much may make the core too hard, giving the ball an unpleasant feel
on impact, whereas too little may lower the rebound.
[0035] The organic peroxide may be a commercially available
product, suitable examples of which include Percumyl D (produced by
NOF Corporation), Perhexa 3M and Perhexa C-40 (NOF Corporation),
and Luperco 231XL (Atochem Co.). These may be used singly or as a
combination of two or more thereof.
[0036] The amount of organic peroxide included per 100 parts by
weight of the base rubber is generally at least 0.1 part by weight,
preferably at least 0.3 part by weight, more preferably at least
0.5 part by weight, and most preferably at least 0.7 part by
weight, but generally not more than 5 parts by weight, preferably
not more than 4 parts by weight, more preferably not more than 3
parts by weight, and most preferably not more than 2 parts by
weight. Too much or too little organic peroxide may make it
impossible to achieve a ball having a good feel on impact,
durability and rebound.
[0037] Examples of suitable inert fillers include zinc oxide,
barium sulfate and calcium carbonate. These may be used singly or
as a combination of two or more thereof.
[0038] The amount of inert filler included per 100 parts by weight
of the base rubber is generally at least 1 part by weight, and
preferably at least 5 parts by weight, but generally not more than
50 parts by weight, preferably not more than 45 parts by weight,
more preferably not more than 40 parts by weight, and most
preferably not more than 35 parts by weight. Too much or too little
inert filler may make it impossible to achieve a proper weight and
a good rebound.
[0039] In addition, an antioxidant may be included if necessary.
Illustrative examples of suitable commercial antioxidants include
Nocrac 200, Nocrac NS-6 and Nocrac NS-30 (both available from Ouchi
Shinko Chemical Industry Co., Ltd.), and Yoshinox 425 (available
from Yoshitomi Pharmaceutical Industries, Ltd.). These may be used
singly or as a combination of two or more thereof.
[0040] The amount of antioxidant included per 100 parts by weight
of the base rubber is generally 0 or more part by weight,
preferably at least 0.05 part by weight, and more preferably at
least 0.1 part by weight, but generally not more than 3 parts by
weight, preferably not more than 2 parts by weight, more preferably
not more than 1 part by weight, and most preferably not more than
0.5 part by weight. Too much or too little antioxidant may make it
impossible to achieve a good rebound and durability.
[0041] To enhance the rebound of the golf ball and increase its
initial velocity, it is preferable to include within the core an
organosulfur compound.
[0042] No particular limitation is imposed on the organosulfur
compound, provided it improves the rebound of the golf ball.
Exemplary organosulfur compounds include thiophenols,
thionaphthols, halogenated thiophenols, and metal salts thereof.
Specific examples include pentachlorothiophenol,
pentafluorothiophenol, pentabromothiophenol, p-chlorothiophenol,
the zinc salt of pentachlorothiophenol, the zinc salt of
pentafluorothiophenol, the zinc salt of pentabromothiophenol, the
zinc salt of p-chlorothiophenol; and diphenylpolysulfides,
dibenzylpolysulfides, dibenzoylpolysulfides,
dibenzothiazoylpolysulfides and dithiobenzoylpolysulfides having 2
to 4 sulfurs. The zinc salt of pentachlorothiophenol is especially
preferred.
[0043] It is recommended that the amount of the organosulfur
compound included per 100 parts by weight of the base rubber be
generally at least 0.05 part by weight, and preferably at least 0.1
part by weight, but generally not more than 5 parts by weight,
preferably not more than 4 parts by weight, more preferably not
more than 3 parts by weight, and most preferably not more than 2.5
parts by weight. If too much organosulfur compound is included, the
effects of addition may peak so that further addition has no
apparent effect, whereas the use of too little organosulfur
compound may fail to confer the effects of such addition to a
sufficient degree.
[0044] Next, the envelope layer is described.
[0045] The envelope layer material has a hardness, expressed as the
Durometer D hardness, which, while not subject to any particular
limitation, is generally at least 50 but not more than 75, more
preferably at least 60 but not more than 70, and even more
preferably at least 62 but not more than 68. If the envelope layer
material is softer than the above range, the ball may have too much
spin receptivity on full shots, as a result of which an increased
distance may not be achieved. On the other hand, if this material
is harder than the above range, the durability of the ball to
cracking under repeated impact may worsen and the ball may have too
hard a feel when played. The envelope layer has a thickness which,
while not subject to any particular limitation, is generally at
least 1.0 mm but not more than 4.0 mm, preferably at least 1.2 mm
but not more than 3.0 mm, and more preferably at least 1.4 mm but
not more than 2.0 mm. Outside of this range, the spin rate-lowering
effect on shots with a driver (W#1) may be inadequate, as a result
of which an increased distance may not be achieved.
[0046] The envelope layer in the present invention is formed
primarily of a resin material. The resin material in the envelope
layer is preferably an ionomer resin. Zinc-neutralized ionomer
resins and sodium-neutralized ionomer resins are especially
preferred, and may be used either singly or as combinations of two
or more such resins. If both types are used in admixture, the
mixing ratio therebetween, expressed as zinc-neutralized
resin/sodium-neutralized resin (weight ratio), is generally from
25/75 to 75/25, preferably from 35/65 to 65/35, and more preferably
from 45/55 to 55/45. Outside of the above range, the rebound may be
too small, preventing the desired distance from being achieved, the
durability to cracking on repeated impact at normal temperatures
may worsen, and the durability to cracking at low temperatures
(below 0.degree. C.) may worsen. Moreover, it is desirable for each
ionomer to have an acid content of generally at least 16 wt %,
preferably at least 17 wt %, and more preferably at least 18 wt %.
The amount of such an ionomer resin included in the envelope
layer-forming material is generally at least 20%, preferably at
least 50%, and more preferably at least 70%. If the acid content of
the ionomer and the ionomer content of the envelope layer-forming
material are too low, the spin rate-lowering effect may be too
small, as a result of which the desired distance may not be
achieved.
[0047] It is preferable for the envelope layer material to have a
higher hardness than the intermediate layer material. In this way,
a sufficient spin rate-lowering effect can be achieved on shots
with a driver (W#1). The difference between the hardness of the
envelope layer material and the hardness of the intermediate layer
material is generally at least 1 but not more than 20, preferably
at least 2 but not more than 15, and even more preferably at least
3 but not more than 10. Outside of the above range, the spin
rate-lowering effect on shots with a driver (W#1) may be
inadequate, as a result of which the desired distance may not be
achieved.
[0048] Next, the intermediate layer is described.
[0049] The intermediate layer material has a hardness, expressed as
the Durometer D hardness, which, although not subject to any
particular limitation, is generally at least 50 but not more than
70, preferably at least 55 but not more than 66, and more
preferably at least 60 but not more than 63. If the intermediate
layer material is softer than the above range, the ball may have
too much spin receptivity on full shots, as a result of which an
increased distance may not be attained. On the other hand, if this
material is harder than the above range, the durability of the ball
to cracking under repeated impact may worsen and the ball may have
too hard a feel when played with a putter or on short approach
shots. The intermediate layer has a thickness which, while not
subject to any particular limitation, is generally at least 0.7 mm
but not more than 2.0 mm, preferably at least 0.9 mm but not more
than 1.7 mm, and more preferably at least 1.1 mm but not more than
1.4 mm. Outside of this range, the spin rate-lowering effect on
shots with a driver (W#1) may be inadequate, as a result of which
an increased distance may not be achieved. Moreover, a thickness
below the foregoing range may lower the durability to cracking on
repeated impact and the low-temperature durability.
[0050] The intermediate layer in the invention may be formed
primarily of a resin material which is the same as or different
from the above-described material used to form the envelope layer.
An ionomer resin is especially preferred. Specific examples include
sodium-neutralized ionomer resins available under the trade name
designations Himilan 1605, Himilan 1601 and Surlyn 8120, and
zinc-neutralized ionomer resins such as Himilan 1557, Himilan 1706
and Himilan 1855. These may be used singly or as a combination of
two or more thereof.
[0051] An embodiment in which the intermediate layer material is
composed primarily of, in admixture, both a zinc-neutralized
ionomer resin and a sodium-neutralized ionomer resin is especially
preferable for attaining the objects of the invention. The mixing
ratio, expressed as zinc-neutralized resin/sodium-neutralized resin
(weight ratio), is generally from 25/75 to 75/25, preferably from
35/65 to 65/35, and more preferably from 45/55 to 55/45. Outside of
the above ratio, the ball rebound may be too low, as a result of
which the desired distance may not be achieved, the durability to
repeated impact at normal temperatures may worsen, and the
durability to cracking at low temperatures (below 0.degree. C.) may
worsen.
[0052] To increase adhesion between the intermediate layer material
and the polyurethane used in the subsequently described cover, it
is desirable to abrade the surface of the intermediate layer. In
addition, it is preferable to apply a primer (adhesive) to the
surface of the intermediate layer following such abrasion or to add
an adhesion reinforcing agent to the intermediate layer material.
Examples of adhesion reinforcing agents that may be incorporated in
the material include organic compounds such as 1,3-butanediol and
trimethylolpropane, and oligomers such as polyethylene glycol and
polyhydroxy polyolefin oligomers. The use of trimethylolpropane or
a polyhydroxy polyolefin oligomer is especially preferred. Examples
of commercially available products include trimethylolpropane
produced by Mitsubishi Gas Chemical Co., Ltd. and polyhydroxy
polyolefin oligomers produced by Mitsubishi Chemical Corporation
(under the trade name designation Polytail H; number of main-chain
carbons, 150 to 200; with hydroxyl groups at the ends).
[0053] Next, the cover is described. As used herein, the term
"cover" denotes the outermost layer of the ball construction, and
excludes what is referred to herein as the intermediate layer and
the envelope layer.
[0054] The cover material has a hardness, expressed as the
Durometer D hardness, which, while not subject to any particular
limitation, is preferably at least 30 but not more than 55, more
preferably at least 40 but nor more than 54, and even more
preferably at least 45 but not more than 53. At a hardness below
this range, the ball tends to take on too much spin on full shots,
as a result of which an increased distance may not be achieved. On
the other hand, at a hardness above this range, on approach shots,
the ball lacks spin receptivity and thus may have an inadequate
controllability even when played by a professional or other skilled
golfer.
[0055] The thickness of the cover, while not subject to any
particular limitation, is preferably at least 0.3 mm but not more
than 1.5 mm, more preferably at least 0.5 mm but not more than 1.3
mm, and even more preferably at least 0.7 mm but not more than 1.1
mm. If the cover is thicker than the above range, the ball may have
an inadequate rebound on shots with a driver (W#1) or the spin rate
may be too high, as a result of which an increased distance may not
be achieved. Conversely, if the cover is thinner than the above
range, the ball may have a poor scuff resistance and inadequate
controllability even when played by a professional or other skilled
golfer.
[0056] From the standpoint of controllability and scuff resistance,
it is preferable for the above cover material to be composed
primarily of polyurethane. For amenability to mass production, it
is especially preferable to use a thermoplastic urethane cover. In
the practice of the invention, the use of a cover-molding material
(C) composed primarily of the following components A and B is
advantageous: [0057] (A) a thermoplastic polyurethane material, and
[0058] (B) an isocyanate mixture obtained by dispersing (b-1) a
compound having two or more isocyanate groups as functional groups
per molecule in (b-2) a thermoplastic resin which is substantially
non-reactive with isocyanate.
[0059] Components (A), (B) and (C) are described below.
(A) Thermoplastic Polyurethane Material
[0060] The thermoplastic polyurethane material has a morphology
which includes soft segments composed of a polymeric polyol
(polymeric glycol) and hard segments composed of a chain extender
and a diisocyanate. The polymeric polyol used as a starting
material may be any that has hitherto been employed in the art
relating to thermoplastic polyurethane materials, without
particular limitation. Exemplary polymeric polyols include
polyester polyols and polyether polyols, although polyether polyols
are better than polyester polyols for synthesizing thermoplastic
polyurethane materials that provide a high rebound resilience and
have excellent low-temperature properties. Suitable polyether
polyols include polytetramethylene glycol and polypropylene glycol.
Polytetramethylene glycol is especially preferred for achieving a
good rebound resilience and good low-temperature properties. The
polymeric polyol has an average molecular weight of preferably
1,000 to 5,000. To synthesize a thermoplastic polyurethane material
having a high rebound resilience, an average molecular weight of
2,000 to 4,000 is especially preferred.
[0061] Preferred chain extenders include those used in the prior
art relating to thermoplastic polyurethane materials. Illustrative,
non-limiting, examples include 1,4-butylene glycol, 1,2-ethylene
glycol, 1,3-butanediol, 1,6-hexanediol, and
2,2-dimethyl-1,3-propanediol. These chain extenders have an average
molecular weight of preferably 20 to 15,000.
[0062] Diisocyanates suitable for use include those employed in the
prior art relating to thermoplastic polyurethane materials.
Illustrative, non-limiting, examples include aromatic diisocyanates
such as 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate
and 2,6-toluene diisocyanate; and aliphatic diisocyanates such as
hexamethylene diisocyanate. Depending on the type of isocyanate
used, the crosslinking reaction during injection molding may be
difficult to control. In the present invention, to ensure stable
reactivity with the subsequently described isocyanate mixture (B),
it is most preferable to use an aromatic diisocyanate, and
specifically 4,4'-diphenylmethane diisocyanate.
[0063] A commercial product may be suitably used as the
above-described thermoplastic polyurethane material. Illustrative
examples include Pandex T-8290, Pandex T-8295 and Pandex T-8260
(all manufactured by DIC Bayer Polymer, Ltd.), and Resamine 2593
and Resamine 2597 (both manufactured by Dainichi Seika Colour &
Chemicals Mfg. Co., Ltd.).
(B) Isocyanate Mixture
[0064] The isocyanate mixture (B) is prepared by dispersing (b-1)
an isocyanate compound having as functional groups at least two
isocyanate groups per molecule in (b-2) a thermoplastic resin which
is substantially non-reactive with isocyanate. Above isocyanate
compound (b-1) is preferably an isocyanate compound used in the
prior art relating to thermoplastic polyurethane materials.
Illustrative, non-limiting, examples include aromatic diisocyanates
such as 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate
and 2,6-toluene diisocyanate; and aliphatic diisocyanates such as
hexamethylene diisocyanate. From the standpoint of reactivity and
work safety, the use of 4,4'-diphenylmethane diisocyanate is most
preferred.
[0065] The thermoplastic resin (b-2) is preferably a resin having a
low water absorption and excellent compatibility with thermoplastic
polyurethane materials. Illustrative, non-limiting, examples of
such resins include polystyrene resins, polyvinyl chloride resins,
ABS resins, polycarbonate resins and polyester elastomers (e.g.,
polyether-ester block copolymers, polyester-ester block
copolymers). From the standpoint of rebound resilience and
strength, the use of a polyester elastomer, particularly a
polyether-ester block copolymer, is especially preferred.
[0066] In the isocyanate mixture (B), it is desirable for the
relative proportions of the thermoplastic resin (b-2) and the
isocyanate compound (b-1), expressed as the weight ratio
(b-2):(b-1), to be from 100:5 to 100:100, and especially from
100:10 to 100:40. If the amount of the isocyanate compound (b-1)
relative to the thermoplastic resin (b-2) is too small, a greater
amount of the isocyanate mixture (B) will have to be added to
achieve an amount of addition sufficient for the crosslinking
reaction with the thermoplastic polyurethane material (A). As a
result, the thermoplastic resin (b-2) will exert a large influence,
compromising the physical properties of the cover-molding material
(C). On the other hand, if the amount of the isocyanate compound
(b-1) relative to the thermoplastic resin (b-2) is too large, the
isocyanate compound (b-1) may cause slippage to occur during
mixing, making preparation of the isocyanate mixture (B)
difficult.
[0067] The isocyanate mixture (B) can be obtained by, for example,
adding the isocyanate compound (b-1) to the thermoplastic resin
(b-2) and thoroughly working together these components at a
temperature of 130 to 250.degree. C. using mixing rolls or a
Banbury mixer, then either pelletizing or cooling and subsequently
grinding. A commercial product such as Crossnate EM30 (made by
Dainichi Seika Colour & Chemicals Mfg. Co., Ltd.) may be
suitably used as the isocyanate mixture (B).
(C) Cover-Molding Material
[0068] The cover-molding material (C) is composed primarily of the
above-described thermoplastic polyurethane material (A) and
isocyanate mixture (B). The relative proportions of the
thermoplastic polyurethane material (A) and the isocyanate mixture
(B) in the cover-molding material (C), expressed as the weight
ratio (A):(B), is preferably from 100:1 to 100:100, more preferably
from 100:5 to 100:50, and even more preferably from 100:10 to
100:30. If too little isocyanate mixture (B) is included relative
to the thermoplastic polyurethane material (A), a sufficient
crosslinking effect will not be achieved. On the other hand, if too
much is included, unreacted isocyanate may discolor the molded
material.
[0069] In addition to the above-described ingredients, other
ingredients may be included in the cover-molding material (C). For
example, thermoplastic polymeric materials other than the
thermoplastic polyurethane material may be included; illustrative
examples include polyester elastomers, polyamide elastomers,
ionomer resins, styrene block elastomers, polyethylene and nylon
resins. Thermoplastic polymeric materials other than the
thermoplastic polyurethane material may be included in an amount of
0 to 100 parts by weight, preferably 1 to 75 parts by weight, and
more preferably 10 to 50 parts by weight, per 100 parts by weight
of the thermoplastic polyurethane material serving as the essential
component. The amount of such thermoplastic polymeric materials
used is selected as appropriate for such purposes as adjusting the
hardness of the cover material, improving the rebound, improving
the flow properties, and improving adhesion. If necessary, various
additives such as pigments, dispersants, antioxidants, light
stabilizers, ultraviolet absorbers and parting agents may also be
suitably included in the cover-molding material (C).
[0070] Formation of the cover from the cover-molding material (C)
can be carried out by adding the isocyanate mixture (B) to the
thermoplastic polyurethane material (A) and dry mixing, then using
an injection molding machine to mold the mixture into a cover over
the core. The molding temperature varies with the type of
thermoplastic polyurethane material (A), although molding is
generally carried out within a temperature range of 150 to
250.degree. C.
[0071] Reactions and crosslinking which take place in the golf ball
cover obtained as described above are believed to involve the
reaction of isocyanate groups with hydroxyl groups remaining on the
thermoplastic polyurethane material to form urethane bonds, or the
creation of an allophanate or biuret crosslinked form via a
reaction involving the addition of isocyanate groups to urethane
groups in the thermoplastic polyurethane material. Although the
crosslinking reaction has not yet proceeded to a sufficient degree
immediately after injection molding of the cover-molding material
(C), the crosslinking reaction can be made to proceed further by
carrying out an annealing step after molding, in this way
maintaining properties useful for a golf ball cover. "Annealing,"
as used herein, refers to heat aging the cover at a constant
temperature for a given length of time, or aging the cover for a
fixed period at room temperature.
[0072] In addition to the above resin components, various optional
additives may be included in the above-described resin materials
for the envelope layer, the intermediate layer and the cover. Such
additives include, for example, pigments, dispersants,
antioxidants, ultraviolet absorbers, ultraviolet stabilizers,
parting agents, plasticizers, and inorganic fillers (e.g., zinc
oxide, barium sulfate, titanium dioxide).
Relationship between Core Surface Hardness and Hardnesses of
Envelope Layer, Intermediate Layer and Cover Materials
[0073] In the present invention, it is critical that the
relationship among the core surface hardness and the hardnesses of
the respective materials for the envelope layer, intermediate layer
and cover, expressed in terms of the Durometer D hardness, satisfy
the conditions: cover material hardness<intermediate layer
material hardness<envelope layer material hardness>core
surface hardness. The reasons are the same as given above in the
description of the envelope layer.
Thickness Relationship Between Envelope Layer, Intermediate Layer
and Cover
[0074] In the present invention, it is critical for the thicknesses
of the envelope layer, the intermediate layer and the cover to
satisfy the relationship
[0075] cover thickness<intermediate layer thickness, and
preferably also the relationship
[0076] cover thickness<intermediate layer thickness<envelope
thickness.
By setting the core diameter to at least 31 mm and also designing
the ball construction so that the relationships among the
thicknesses of the envelope layer, intermediate layer and cover are
as indicated above, there can be obtained a golf ball which
exhibits a good flight performance, good controllability and a good
feel when played. Should the cover be thicker than the intermediate
layer, the ball rebound will decrease or the ball will have
excessive spin receptivity on full shots, as a result of which an
increased distance will not be attainable. Should the envelope
layer be thinner than the intermediate layer, the spin
rate-lowering effect will be inadequate, preventing the desired
distance from being achieved.
[0077] The multi-piece solid golf ball of the invention can be
manufactured using an ordinary process such as a known injection
molding process to form on top of one another the respective layers
described above--the core, envelope layer, intermediate layer, and
cover. For example, a molded and vulcanized article composed
primarily of the rubber material may be placed as the core within a
particular injection-molding mold, following which the envelope
layer material and the intermediate layer material may be
injection-molded in this order to give an intermediate spherical
body. The spherical body may then be placed within another
injection-molding mold and the cover material injection-molded over
the spherical body to give a multi-piece golf ball. Alternatively,
the cover may be formed as a layer over the intermediate spherical
body by, for example, placing two half-cups, molded beforehand as
hemispherical shells, around the intermediate spherical body so as
to encase it, then molding under applied heat and pressure.
[0078] Numerous dimples may be formed on the surface of the cover.
The dimples arranged on the cover surface, while not subject to any
particular limitation, number preferably at least 280 but not more
than 360, more preferably at least 300 but not more than 350, and
even more preferably at least 320 but not more than 340. If the
number of dimples is higher than the above range, the ball will
tend to have a low trajectory, which may shorten the distance of
travel. On the other hand, if the number of dimples is too small,
the ball will tend to have a high trajectory, as a result of which
an increased distance may not be achieved.
[0079] Any one or combination of two or more dimple shapes,
including circular shapes, various polygonal shapes, dewdrop shapes
and oval shapes, may be suitably used. If circular dimples are
used, the diameter of the dimples may be set to at least about 2.5
mm but not more than about 6.5 mm, and the depth may be set to at
least 0.08 mm but not more than 0.30 mm.
[0080] To fully manifest the aerodynamic characteristics of the
dimples, the dimple coverage on the spherical surface of the golf
ball, which is the sum of the individual dimple surface areas, each
defined by the border of the flat plane circumscribed by the edge
of the dimple, expressed as a ratio (SR) with respect to the
spherical surface area of the ball were it to be free of dimples,
is preferably at least 60% but not more than 90%. Also, to optimize
the trajectory of the ball, the value V.sub.0 obtained by dividing
the spatial volume of each dimple below the flat plane
circumscribed by the edge of that dimple by the volume of a
cylinder whose base is the flat plane and whose height is the
maximum depth of the dimple from the cylinder base is preferably at
least 0.35 but not more than 0.80. In addition, the VR value, which
is the sum of the volumes of individual dimples formed below flat
planes circumscribed by the dimple edges, as a percentage of the
volume of the ball sphere were it to have no dimples thereon, is
preferably at least 0.6% but not more than 1%. Outside of the above
ranges for these values, the ball may assume a trajectory that is
not conducive to achieving a good distance, as a result of which
the ball may fail to travel a sufficient distance when played.
[0081] The golf ball of the invention, which can be manufactured so
as to conform with the Rules of Golf for competitive play, may be
produced to a ball diameter which is of a size that will not pass
through a ring having an inside diameter of 42.672 mm, but is not
more than 42.80 mm, and to a weight of generally from 45.0 to 45.93
g.
[0082] As explained above, by using primarily a polyurethane
material in the cover, by optimizing the respective thicknesses and
hardnesses of the envelope layer, intermediate layer and cover as
described above, and by setting the core diameter to at least a
particular size, the inventive golf ball having a multi-layer
construction is highly beneficial for professionals and other
skilled golfers because the spin rate of the ball on full shots
with a driver is lowered, providing an increased distance of travel
and a good controllability, and because the ball has an excellent
durability to cracking under repeated impact and an excellent scuff
resistance.
EXAMPLES
[0083] Examples of the invention and Comparative Examples are given
below by way of illustration, and not by way of limitation.
Examples 1 and 2, Comparative Examples 1 to 6
Core Formation
[0084] Rubber compositions were formulated as shown in Table 1,
then molded and vulcanized under the conditions shown in the table
to form cores. Numbers shown for the ingredients in the table
indicate parts by weight.
TABLE-US-00001 TABLE 1 Example Comparative Example 1 2 1 2 3 4 5 6
Core Polybutadiene 100 100 100 100 100 100 100 100 formulation Zinc
acrylate 28.1 24.6 28.1 24.6 24.6 31.2 24.6 31.0 Peroxide (1) -- --
-- -- -- -- -- 0.3 Peroxide (2) 1.2 1.2 1.2 1.2 1.2 1.2 1.2 0.3
Antioxidant 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Zinc oxide 30.6 31.9
34.5 64.2 22.5 12.8 28.8 22.4 Zinc salt of 2 2 2 2 2 2 2 0.2
pentachlorothiophenol Zinc stearate 5 5 5 5 5 5 5 5 Vulcanization
Temperature (.degree. C.) 155 155 155 155 155 155 155 155
conditions Time (min) 15 15 15 15 15 15 15 15
[0085] Trade names for some the materials appearing in the table
are given below. [0086] Polybutadiene: Available from JSR
Corporation under the trade name BR730. Synthesized with a
neodymium catalyst. [0087] Peroxide (1): Dicumyl peroxide,
available from NOF Corporation under the trade name Percumyl D.
[0088] Peroxide (2): A mixture of 1,1-di(t-butylperoxy)cyclohexane
and silica, available from NOF Corporation under the trade name
Perhexa C-40. [0089] Antioxidant:
2,2-Methylenebis(4-methyl-6-butylphenol), available from Ouchi
Shinko Chemical Industry Co., Ltd. as Nocrac NS-6. [0090] Sulfur:
Zinc white-sulfur mixture, available from Tsurumi Chemical Industry
Co., Ltd.
Formation of Envelope Layer, Intermediate Layer and Cover
[0091] Next, the envelope layer, intermediate layer and cover
formulated from the various resin components shown in Table 2 were
injection-molded, thereby forming over the core, in order: an
envelope layer, an intermediate layer and a cover. Next, the
dimples shown in Table 3, which were common to all the examples,
were formed on the cover surface, thereby producing multi-piece
solid golf balls.
TABLE-US-00002 TABLE 2 No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7
Himilan 1605 50 68.75 Himilan 1557 15 30 Himilan 1706 35 Himilan
1855 20 AM 7317 50 AM 7318 50 AM 7311 50 Dynaron 6100P 31.25 Hytrel
3046 100 Behenic acid 18 Calcium hydroxide 2.3 Calcium stearate
0.15 Zinc stearate 0.15 Trimethylolpropane 1.1 Polytail H 2 T-8295
94.8 T-8260 94.8 Titanium oxide 2 2.2 3.8 3.8 Polyethylene wax 1.4
1.4 Isocyanate compound 18 18 Note: Numbers in the table indicate
parts by weight.
[0092] Trade names for the chief materials appearing in Table 2 are
given below. [0093] Himilan: Ionomer resins produced by
DuPont-Mitsui Polychemicals Co., Ltd. [0094] AM 7317: A
high-stiffness zinc ionomer resin having an acid content of 18%
produced by DuPont-Mitsui Polychemicals Co., Ltd. [0095] AM 7318: A
high-stiffness sodium ionomer resin having an acid content of 18%
produced by DuPont-Mitsui Polychemicals Co., Ltd. [0096] AM 7317:
An ionomer resin produced by DuPont-Mitsui Polychemicals Co., Ltd.
[0097] Dynaron: A hydrogenated polymer produced by JSR Corporation.
[0098] Hytrel: A polyester elastomer produced by DuPont-Toray Co.,
Ltd. [0099] Behenic acid: NAA222-S (beads), produced by NOF
Corporation. [0100] Calcium hydroxide: CLS-B, produced by Shiraishi
Kogyo. [0101] Trimethylolpropane: Produced by Mitsubishi Gas
Chemical Co., Inc. [0102] Polytail H: A low-molecular-weight
polyolefin polyol produced by Mitsubishi Chemical Corporation.
[0103] T-8260, T-8295: MDI-PTMG type thermoplastic polyurethane
produced by DIC Bayer Polymer under the trademark designation
Pandex. [0104] Polyethylene wax: Produced by Sanyo Chemical
Industries, Ltd. under the trade name Sanwax 161P. [0105]
Isocyanate compound: Crossnate EM30 (trade name), an isocyanate
masterbatch which is produced by Dainichi Seika Colour &
Chemicals Mfg. Co., Ltd., contains 30% of 4,4'-diphenylmethane
diisocyanate (measured concentration of amine reverse-titrated
isocyanate according to JIS-K1556, 5 to 10%), and in which the
masterbatch base resin is a polyester elastomer. The isocyanate
compound was mixed with Pandex at the time of injection
molding.
TABLE-US-00003 [0105] TABLE 3 Diameter Depth No. Number of dimples
(mm) (mm) V.sub.0 SR VR 1 12 4.6 0.15 0.47 0.81 0.783 2 234 4.4
0.15 0.47 3 60 3.8 0.14 0.47 4 6 3.5 0.13 0.46 5 6 3.4 0.13 0.46 6
12 2.6 0.10 0.46 Total 330
Dimple Definitions
[0106] Diameter: Diameter of flat plane circumscribed by edge of
dimple. [0107] Depth: Maximum depth of dimple from flat plane
circumscribed by edge of dimple. [0108] V.sub.0: Spatial volume of
dimple below flat plane circumscribed by dimple edge, divided by
volume of cylinder whose base is the flat plane and whose height is
the maximum depth of dimple from the base. [0109] SR: Sum of
individual dimple surface areas, each defined by the border of the
flat plane circumscribed by the edge of the dimple, as a percentage
of surface area of ball sphere were it to have no dimples thereon.
[0110] VR: Sum of volumes of individual dimples formed below flat
plane circumscribed by the edge of the dimple, as a percentage of
volume of ball sphere were it to have no dimples thereon.
[0111] The golf balls obtained in Examples 1 and 2 of the invention
and Comparative Examples 1 to 6 were tested and evaluated according
to the criteria described below with regard to the following:
surface hardness and other physical properties of each layer and of
the ball, flight performance, spin rate on approach shots
(controllability), and scuff resistance. The results are shown in
Table 4. All measurements were carried out in a 23.degree. C.
atmosphere.
(1) Core Deflection
[0112] The core was placed on a hard plate, and the deflection (mm)
by the core when compressed under a final load of 1,275 N (130 kgf)
from an initial load of 98 N (10 kgf) was measured.
(2) Surface Hardness of Core
[0113] The surface of the core is spherical. The durometer indenter
was set substantially perpendicular to this spherical surface, and
Durometer D hardness measurements (using a type D durometer in
accordance with ASTM-2240) were taken at two randomly selected
points on the surface of the core. The average of the two
measurements was used as the core surface hardness.
(3) Hardness of Envelope Layer Material
[0114] The resin material for the envelope layer was formed into a
sheet having a thickness of about 2 mm, and the hardness was
measured with a type D durometer in accordance with ASTM D2240.
(4) Hardness of Intermediate Layer Material
[0115] The same method of measurement was used as in (3) above.
(5) Hardness of Cover Material
[0116] The same method of measurement was used as in (3) above.
(6) Ball Deflection
[0117] The ball was placed on a hard plate, and the deflection (mm)
by the ball when compressed under a final load of 1,275 N (130 kgf)
from an initial load of 98 N (10 kgf) was measured. Ball deflection
was measured only in Examples 1 and 2.
(7) Flight
[0118] The carry and total distance of the ball when hit at a head
speed (HS) of 45 m/s with a driver (abbreviated below as "W#1";
TourStage X-Drive Type 405, manufactured by Bridgestone Sports Co.,
Ltd.; loft angle, 9.5.degree.) mounted on a swing robot were
measured. The results were rated according to the criteria
indicated below. The spin rate, which was measured with an
apparatus for measuring initial conditions, was the value obtained
for the ball immediately following impact. [0119] Good: Total
distance was 232.0 m or more [0120] NG: Total distance was less
than 232.0 m
(8) Spin Rate on Approach Shots
[0121] The spin rate of a ball hit at a head speed of 22 m/s with a
sand wedge (abbreviated below as "W"; J's Classical Edition,
manufactured by Bridgestone Sports Co., Ltd.) was measured. The
results were rated according to the criteria indicated below. The
spin rate was measured by the same method as that used above when
measuring distance. [0122] Good: Spin rate was at least 6,600 rpm
[0123] Fair: Spin rate was at least 6,300 rpm but less than 6,600
rpm [0124] NG: Spin rate was less than 6,300 rpm
(9) Scuff Resistance
[0125] A non-plated pitching sand wedge was set in a swing robot,
and the ball was hit once at a head speed of 40 m/s, following
which the surface state of the ball was visually examined and rated
as follows. [0126] Good: Can be used again [0127] NG: Cannot be
used again
TABLE-US-00004 [0127] TABLE 4 Example Comparative Example 1 2 1 2 3
4 5 6 Core Diameter (mm) 34.9 34.9 34.9 29.0 34.9 34.9 34.9 37.3
Weight (g) 27.2 27.1 28.0 18.0 26.4 25.5 27.2 31.7 Deflection (mm)
4.4 4.9 4.4 4.9 4.4 3.3 4.9 3.1 Surface hardness (D) 48 45 48 45 48
55 45 56 Envelope Material No. 1 No. 1 No. 1 No. 1 No. 1 No. 2 No.
1 -- layer Thickness (mm) 1.7 1.7 1.7 4.7 1.1 1.7 1.7 -- material
Specific gravity 0.96 0.96 0.96 0.96 0.96 1.07 0.96 -- Material
hardness (D) 66 66 66 66 66 30 66 -- Sphere Outside diameter (mm)
38.4 38.4 38.4 38.4 37.2 38.4 38.4 -- encased by Weight (g) 34.1
34.1 35.0 34.1 30.8 33.3 34.2 -- envelope layer Intermediate
Material No. 3 No. 3 No. 3 No. 3 No. 3 No. 3 No. 4 No. 3 layer
Thickness (mm) 1.15 1.15 1.15 1.15 0.95 0.35 1.15 1.67 material
Specific gravity 0.95 0.95 0.95 0.95 0.95 0.95 0.93 0.95 Material
hardness (D) 62 62 62 62 62 62 56 62 Sphere Outside diameter (mm)
40.7 40.7 40.7 40.7 39.1 39.1 40.7 40.6 encased by Weight (g) 39.4
39.4 40.4 39.5 34.9 34.9 39.4 39.3 intermediate layer Cover
Material No. 6 No. 6 No. 5 No. 6 No. 6 No. 6 No. 7 No. 6 material
Thickness (mm) 1.00 1.00 1.00 1.00 1.80 1.80 1.00 1.03 Specific
gravity 1.13 1.13 0.96 1.13 1.13 1.13 1.13 1.13 Material hardness
(D) 53 53 53 53 53 53 58 53 Ball.sup.1) Diameter (mm) 42.7 42.7
42.7 42.7 42.7 42.7 42.7 42.7 Weight (g) 45.5 45.5 45.5 45.5 45.5
45.4 45.5 45.5 Flight Spin rate (rpm) 2894 2749 2724 3177 2816 2985
2705 2856 W#1 Carry (m) 222.0 220.5 220.1 214.6 217.2 216.2 218.5
219.2 HS: 45 m/s Total distance (m) 236.4 235.3 235.1 227.7 230.3
228.5 234.0 230.5 Rating good good good NG NG NG good NG SW Spin
rate (rpm) 6977 6955 6554 7008 6912 6950 6037 6962 HS: 22 m/s
Rating good good fair good good good good good Scuff resistance
good good NG good good good NG good .sup.1)The measured deflection
of the ball was 2.2 mm in Example 1, and 2.4 mm in Example 2.
[0128] From the results in Table 4, the golf balls obtained in
Comparative Examples 1 to 6 were inferior to the balls obtained
according to the invention (Examples 1 and 2) in the following
respects.
[0129] In Comparative Example 1, because the cover was made of an
ionomer resin, the ball had a low scuff resistance and was not
receptive to spin on approach shots.
[0130] In Comparative Example 2, because the core diameter was less
than 31 mm, on shots taken with a driver (W#1), the spin rate rose
and an increased distance was not achieved.
[0131] In Comparative Example 3, because the cover layer was
thicker than the intermediate layer, on shots taken with a driver
(W#1), the spin rate rose and an increased distance was not
achieved.
[0132] In Comparative Example 4, because the envelope layer was
softer than the intermediate layer, on shots taken with a driver
(W#1), the spin rate rose and an increased distance was not
achieved.
[0133] In Comparative Example 5, because the cover layer was harder
than the intermediate layer, the ball had a poor scuff resistance
and lacked a sufficient spin rate on approach shots.
[0134] The ball in Comparative Example 6 was a three-piece golf
ball which lacked an envelope layer; that is, the core was encased
by only two layers. In this ball, the spin rate remained too high,
as a result of which an increased distance was not achieved.
* * * * *