U.S. patent application number 10/254563 was filed with the patent office on 2003-06-19 for solid golf ball.
Invention is credited to Yokota, Masatoshi.
Application Number | 20030114246 10/254563 |
Document ID | / |
Family ID | 19116065 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030114246 |
Kind Code |
A1 |
Yokota, Masatoshi |
June 19, 2003 |
Solid golf ball
Abstract
A solid golf ball with a polyurethane cover is provided which is
satisfactory in the moldability of the cover and in ball
characteristics such as a shot feeling and a flight distance. The
solid golf ball of the invention includes a solid center, an
intermediate layer, and a polyurethane cover. A material having a
flexural modulus of from 150 to 420 MPa is used for the
intermediate layer in order for the golf ball to offer satisfactory
shot feeling and flight distance. By the use of a vulcanizate of a
rubber composition containing a diphenyl disulfide for the solid
center, the golf ball can exhibit an increased flight distance. In
order to enhance the moldability of the cover a urethane prepolymer
having a residual isocyanate monomer content of not more than 0.5%
by mass is used.
Inventors: |
Yokota, Masatoshi;
(Kobe-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
19116065 |
Appl. No.: |
10/254563 |
Filed: |
September 26, 2002 |
Current U.S.
Class: |
473/351 |
Current CPC
Class: |
A63B 37/0086 20130101;
A63B 37/0033 20130101; C08G 18/10 20130101; A63B 37/0003 20130101;
A63B 37/0031 20130101; A63B 37/0064 20130101; A63B 37/0049
20130101; A63B 37/04 20130101; C08G 18/10 20130101; C08G 18/4854
20130101; A63B 37/0045 20130101; C08G 18/3814 20130101 |
Class at
Publication: |
473/351 |
International
Class: |
A63B 037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 26, 2001 |
JP |
2001-294466 |
Claims
What is claimed is:
1. A solid golf ball comprising a solid center, an intermediate
layer, and a polyurethane cover, wherein the solid center has an
outer diameter of from 36.7 mm to 40.8 mm; the intermediate layer
has a thickness of from 0.5 mm to 1.5 mm and is formed from a
material having a flexural modulus of from 150 to 420 MPa; and the
polyurethane cover has a thickness of from 0.5 mm to 1.5 mm and is
formed from a cured product of a composition comprising an
isocyanate group-terminated urethane prepolymer and an aromatic
polyamine compound, the cured product having a Shore D hardness of
from 35 to 55.
2. The solid golf ball according to claim 1, wherein the isocyanate
group-terminated urethane prepolymer has a residual isocyanate
monomer content of not more than 0.5% by mass.
3. The solid golf ball according to claim 2, wherein the isocyanate
group-terminated urethane prepolymer has a residual isocyanate
monomer content of not more than 0.1% by mass.
4. The solid golf ball according to claim 1, wherein the isocyanate
group-terminated urethane prepolymer has an isocyanate component
comprising at least one selected from the group consisting of
tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and
paraphenylene diisocyanate.
5. The solid golf ball according to claim 1, wherein the isocyanate
group-terminated urethane prepolymer has an polyol component
comprising polyoxytetramethyleneglycol.
6. The solid golf ball according to claim 1, wherein the aromatic
polyamine compound is
2,2'-dichloro-3,3',5,5'-tetraethyl-4,4'diaminodiphe nylmethane.
7. The solid golf ball according to claim 1, wherein the solid
center has a deformation amount of from 2.8 mm to 3.5 mm when
applying a load from 98N as an initial load to 1275 N as a final
load, and is formed by vulcanizing a rubber composition which
comprises cis-1,4-polybutadiene, an organic peroxide, a
co-crosslinking agent, and an organic sulfur compound represented
by the general formula: 2wherein each of X.sup.1 to X.sup.10 is any
one selected from the group consisting of a hydrogen atom, a
chlorine atom, a bromine atom, an iodine atom, and a cyano group,
and X.sup.1 to X.sup.10 are same or different each other.
8. The solid golf ball according to claim 7, wherein the organic
sulfur compound is diphenyl disulfide or bis(pentachlorophenyl)
disulfide.
9. The solid golf ball according to claim 1, wherein the solid
center has the outer diameter of 38 mm to 40 mm.
10. The solid golf ball according to claim 1, wherein the
intermediate layer has a thickness of from 0.7 mm to 1.2 mm and is
formed from the material having the flexural modulus of from 200
MPa to 400 MPa.
11. The solid golf ball according to claim 1, wherein the
polyurethane cover has the thickness of 0.7 mm to 1.3 mm.
12. The solid golf ball according to claim 1, wherein the cured
product has the Shore D hardness of from 40 to 52.
13. The solid golf ball according to claim 1, wherein the material
having the flexural modulus of from 150 MPa to 420 MPa is an
ionomer resin.
14. A solid golf ball comprising a solid center, an intermediate
layer, and a polyurethane cover, wherein the solid center has an
outer diameter of from 36.7 mm to 40.8 mm; the intermediate layer
has a thickness of from 0.5 mm to 1.5 mm and is formed from an
ionomer resin having a flexural modulus of from 150 MPa to 420 MPa;
and the polyurethane cover has a thickness of from 0.5 mm to 1.5 mm
and is formed by curing a polyurethane composition, the cured
composition having a Shore D hardness of from 35 to 55, wherein the
solid center is formed by vulcanizing a rubber composition which
comprises cis-1,4-polybutadiene, an organic peroxide, a
co-crosslinking agent, and diphenyl disulfide or
bis(pentachlorophenyl) disulfide; the polyurethane cover
composition comprises an isocyanate group-terminated urethane
prepolymer including tolylenediisocyanate as isocyanate component
and polyoxytetramethylenegly- col as polyol component, and an
aromatic polyamine compound.
15. The solid golf ball according to claim 14, wherein the
isocyanate group-terminated urethane prepolymer has a residual
isocyanate monomer content of not more than 0.5% by mass.
16. The solid golf ball according to claim 15, wherein the aromatic
polyamine compound is
2,2'-dichloro-3,3',5,5'-tetraethyl-4,4'-diaminodiph- enylmethane.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a multi-piece solid golf
ball comprising a solid center, an intermediate layer and a
polyurethane cover.
[0003] 2. Description of the Related Art
[0004] An ionomer resin cover is mainly used for a cover of a solid
golf ball employing vulcanized rubber body as a solid core because
the ionomer resin cover has superior durability. The golf ball with
the ionomer resin cover, however, gives a golfer a larger impact
upon shot than do a golf ball with Balata rubber cover, and hence
is likely to impart an inferior shot feeling to the golfer.
[0005] In attempt to improve the shot feeling of the golf ball with
the ionomer cover, Japanese Patent No. 2709950, for example, has
proposed a mixed ionomer cover formed from a mixture of a hard
ionomer comprising a sodium salt or zinc salt of an
olefin-unsaturated carboxylic acid copolymer and a soft ionomer
comprising a sodium salt or zinc salt of an olefin-unsaturated
carboxylic acid-unsaturated carboxylic acid ester terpolymer.
Blending of such a soft ionomer in a cover enables to render the
shot feeling soft, but on the other hand, sacrifices the advantages
inherent to the ionomer cover; for example, the abrasion resistance
(scratching resistance) as well as the repulsion property of the
golf ball.
[0006] In recent years, polyurethane has been focused on as an
inexpensive cover material that imparts to the golfer a shot
feeling analogous to that imparted by the Balata cover and has
higher durability than the Balata cover. For example, the golf ball
with the following polyurethane cover has been proposed.
[0007] In view of a problem that the molding of the polyurethane
cover is difficult because the reaction between a urethane
prepolymer and a polyamine curing agent proceeds rapidly to cause a
steep increase in viscosity, Japanese Patent No. 2662909 has
disclosed a polyurethane cover formed by curing a urethane
prepolymer with a slow-reactive polyamine curing agent. In Japanese
Patent No. 2662909, the steep increase in viscosity due to the
rapid reaction between the urethane prepolymer and the polyamine
curing agent is prevented by the use of the slow-reactive polyamine
curing agent. However, in case of some kinds of urethane
prepolymer, some kinds of curing agent, some combinations of
urethane prepolymer and curing agent, or the like, the increase in
viscosity is still rapid, and thus the molding of the cover is
difficult. Even if the molding of the cover is possible, a golf
ball with the resulting cover is not sufficient in terms of the
repulsion property, spin performance and abraision
reisistance(scrathcing resistance). Thus, further improvements are
desired.
[0008] Japanese unexamined patent publication No. H09-215778 has
proposed a cover formed using a thermoplastic polyurethane
elastomer. Such a thermoplastic polyurethane elastomer used as a
cover material is superior in moldability to the two-part curing
type polyurethane covers, but are inferior in wear resistance, tear
strength and scratching resistance to the two-part curing type
polyurethane cover or the ionomer cover, because of the lack of
three-dimensionally crosslinking points.
[0009] Japanese unexamined patent publication No. 2000-513609 has
proposed a golf ball with a double-layered cover. The
double-layered cover comprises a thermosetting polyurethane cover
having a thickness of less than 0.127 cm as an outer layer and a
cover material having a high flexural modulus as an inner layer.
This golf ball provides a satisfactory flight distance upon a
driver shot for long distance and exhibits satisfactory spin
performance upon a wedge shot for short distance. However, the golf
ball has a problem of a hard feeling imparted to the golfer upon
shot (hereinafter referred to as "hard shot feeling") because of
the too hard inner cover material, and the like problems.
[0010] The present invention has been made in view of the foregoing
circumstances. Accordingly, it is an object of the present
invention to provide a solid golf ball with a polyurethane cover,
which satisfies the moldability of the cover, and the, shot feeling
and the flight distance.
SUMMARY OF THE INVENTION
[0011] According to the present invention, there is provided a
solid golf ball comprising a solid center, an intermediate layer,
and a polyurethane cover, wherein: the solid center has an outer
diameter of from 36.7 to 40.8 mm; the intermediate layer has a
thickness of from 0.5 to 1.5 mm and is formed from a material
having a flexural modulus of from 150 to 420 MPa; and the
polyurethane cover has a thickness of from 0.5 to 1.5 mm and is
formed from a cured product of a composition comprising an
isocyanate group-terminated urethane prepolymer and an aromatic
polyamine compound, the cured product having a Shore D hardness of
from 35 to 55.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] The present invention will now be described in detail. The
solid golf ball of the present invention is characterized by
comprising a solid center, an intermediate layer, and a
polyurethane cover, wherein: the solid center has an outer diameter
of from 36.7 mm to 40.8 mm; the intermediate layer has a thickness
of from 0.5 to 1.5 mm and is formed from a material having a
flexural modulus of from 150 MPa to 420 MPa; and the polyurethane
cover has a thickness of from 0.5 mm to 1.5 mm and is formed from a
cured product of a composition comprising an isocyanate
group-terminated urethane prepolymer and an aromatic polyamine
compound (hereinafter referred to as "polyurethane cover
composition"), the cured product having a Shore D hardness of from
35 to 55.
[0013] First of all, the polyurethane cover used in the present
invention is described. The polyurethane cover is formed from the
cured product of the polyurethane cover composition, which
comprises the isocyanate group-terminated urethane prepolymer and
the aromatic polyamine compound. The isocyanate group-terminated
urethane prepolymer used in the present invention may include any
isocyanate group-terminated urethane prepolymer, without any
particular limitation, as long as it has at least two isocyanate
groups in the urethane prepolymer molecular chain thereof. The
isocyanate group-termnated urethane prepolymer can have each
isocyanate group at the terminal of the backbone chain of the
urethane prepolymer molecular chain or at the terminal of a side
chain thereof, without limitation.
[0014] The isocyanate group-terminated urethane prepolymer is
prepared by allowing a polyol and a polyisocyanate compound to
react with each other under the condition that the isocyanate group
of the polyisocyanate compound is in excess relative to the
hydroxyl group of the polyol in molar ratio. In the present
invention, the residual polyisocyanate monomer content contained in
the isocyanate group-terminated urethane prepolymer is preferably
not more than 0.5% by mass, more preferably not more than 0.1% by
mass. The "residual polyisocyanate monomer", as used herein, means
an unreacted polyisocyanate compound remaining in the isocyanate
group-terminated urethane prepolymer. For example, an excess of the
polyisocyanate compound used for the preparation of the isocyanate
group-terminated urethane prepolymer partially remains unreacted
therein. If the residual polyisocyanate monomer content is more
than 0.5% by mass, a precipitate is likely to be generated in the
polyurethane cover composition. Although the mechanism of the
formation of the precipitate is not apparent, it is presumed that
the reaction product of the residual polyisocyanate monomer and the
polyamine curing agent precipitates. The precipitation causes the
non-uniform reaction between the isocyanate group-terminated
urethane prepolymer and the aromatic polyamine compound, resulting
in difficulty in manufacturing a uniform polyurethane cover.
Non-uniformity of the polyurethane cover affects the durability of
the cover; particularly, it causes to lower the abrasion resistance
(scratching resistance) of the cover. In an extreme case, the
polyurethane cover composition is cured before manufacturing the
polyurethane cover, and thus it is substantially impossible to mold
the polyurethane cover composition.
[0015] The residual polyisocyanate monomer content of the
isocyanate group-terminated urethane prepolymer is defined by the
expression: (the mass of the residual polyisocyanate monomer in the
isocyanate group-terminated urethane prepolymer/the total mass of
the isocyanate group-terminated urethane prepolymer).times.100 and
can be determined by gas chromatography. Examples of specific
isocyanate group-terminated urethane prepolymers having a residual
polyisocyanate monomer content of not more than 0.5% by mass are
ADIPRENE LF600D, ADIPRENE LF800A, ADIPRENE LF900A, and ADIPRENE
LF950A, which are commercially available from UNIROYAL CO.
[0016] The isocyanate group-terminated urethane prepolymer
comprises a conventional polyisocyanate compound as an isocyanate
component. Examples of the polyisocyanate compound are an aromatic
diisocyanate such as 2,4-tolylene diisocyanate, 2,6-tolylene
diisocyanate, or mixtures thereof (TDI), 4,4'-diphenylmethane
diisocyanate or a polynuclear compound thereof, 1,5-naphthylene
diisocyanate (NDI), 3,3'-bitolylene-4,4'-diisocy- anate (TODI),
xylylene diisocyanate (XDI), and paraphenylene diisocyanate (PPDI);
and an alicyclic or aliphatic diisocyanate such as
4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI),
hexamethylene diisocyanate (HDI) and isophorone diisocyanate
(IPDI). These may be used either alone or as a mixture of at least
two of them. Preferably, the isocyanate component comprises at
least one selected from the group consisting of tolylene
diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), and
paraphenylene diisocyanate (PPDI) because the resulting
polyurethane cover has favorable mechanical properties and because
the golf ball with the resulting polyurethane cover has the
sufficient repulsion property, weather resistance and water
resistance.
[0017] The isocyanate group-terminated urethane prepolymer contains
any conventional polyol as a polyol component. The polyol has no
limitation as to whether the polyol has low-molecular-weight or
high-molecular-weight, as long as it has a plurality of hydroxyl
groups. Examples of the low-molecular-weight polyols are a diol
such as ethylene glycol, diethylene glycol, triethylene glycol,
1,3-butanediol, 1,4-butanediol, neopentyl glycol, and
1,6-hexanediol; and a triol such as glycerin, trimethylolpropane,
and hexanetriol. Examples of the high-molecular-weight polyols are
a polyetherpolyol generally resulting from the reaction between an
initiator having active hydrogen and alkylene oxide; a condensed
polyesterpolyol generally resulting from the condensation between a
dibasic acid, such as adipic acid, and a glycol or a triol; a
lactone polyesterpolyol generally resulting from ring opening
polymerization of a lactam such as .epsilon.-caprolactam; a
polycarbonate diol generally synthesized using a cyclic diol; and a
polymer polyol, such as an acrylic polyol, generally prepared by
introducing an appropriate hydroxyl group into an acrylic
copolymer. Examples of specific polyetherpolyols are
polyoxyethylene glycol(PEG), polyoxypropylene glycol (PPG), and
polyoxytetramethylene glycol (PTMG). Examples of specific condensed
polyesterpolyols are polyethylene adipate (PEA), polybutylene
adipate (PBA), and polyhexamethylene adipate (PHMA). Examples of
specific lactone polyesterpolyols are poly-.epsilon.-caprolac- tone
(PCL). In view of their superior repulsion property and water
resistance, polyetherpolyols are preferable. Use of
polyoxytetramethylene glycol is particularly preferable.
[0018] The isocyanate group-terminated urethane prepolymer is
preferably at least one selected from the group consisting of a
tolylene diisocyanate urethane prepolymer, a MDI urethane
prepolymer, and a PPDI urethane prepolymer. The "tolylene
diisocyanate urethane prepolymer", as used herein, means the
isocyanate group-terminated urethane prepolymer resulting from the
reaction between tolylene diisocyanate or a polyisocyanate
comprising tolylene diisocyanate as a major component and a polyol
(preferably polyoxytetramethylene glycol). The "MDI urethane
prepolymer", as used herein, means the isocyanate group-terminated
urethane prepolymer resulting from the reaction between MDI or a
polyisocyanate comprising MDI as a major component and a polyol
(preferably polytetramethylene glycol). The "PPDI urethane
prepolymer", as used herein, means the isocyanate group-terminated
urethane prepolymer resulting from the reaction between PPDI or a
polyisocyanate comprising PPDI as a major component and a polyol
(preferably polytetramethylene glycol).
[0019] The aromatic polyamine compound used in the present
invention has no limitation, as long as it has at least two amino
groups directly or indirectly bonded to an aromatic ring. Herein,
the "indirectly bond to the aromatic ring", for example, means that
the amino group is bonded to the aromatic ring through a sulfide
bond or a lower alkylene bond. Further, the aromatic polyamine
compound may include a monocyclic aromatic polyamine compound
having at least two amino groups bonded to one aromatic ring or a
polycyclic aromatic polyamine compound having at least two
aminophenyl groups each having at least one amino group bonded to
one aromatic ring.
[0020] Examples of the monocyclic aromatic polyamine compounds are
a type such as phenylenediamine, toluenediamine or
diethyltoluenediamine where amino groups are directly bonded to an
aromatic ring; a type such as dimethylthiotoluenediamine where
amino groups are bonded to an aromatic ring through a sulfide bond;
and a type such as xylylenediamine where amino groups are bonded to
an aromatic ring through a lower alkylene group. Use of
dimethylthiotoluenediamine or diethyltoluenediamine is particularly
preferable because they have moderate reactivity with the
isocyanate group-terminated urethane prepolymer.
[0021] The polycyclic aromatic polyamine compound may include
polyaminobenzene having at least two aminophenyl groups directly
bonded to each other or a compound having two aminophenyl groups
bonded to each other through a lower alkylene group or an alkylene
oxide group. Among them, diaminodiphenylalkane having two
aminophenyl groups bonded to each other through a lower alkylene
group is preferable. Typically preferred are
4,4'-diaminodiphenylmethane and derivatives thereof. With such a
compound, benzene nuclei forming hard segments can be arranged
side-by-side linearly on a plane if the compound is of para-form
and has a not very long molecular chain intervening between
aminophenyl groups, and hence it is possible to efficiently make
use of the intermolecular cohesive energy based on urethane bond,
urea bond, hydrogen bond between benzene nuclei, thus resulting in
the improved repulsion property, tensile strength and tear
strength. For this reason, the resulting cover tends to be improved
in cover strength and cover durability such as abraision
resistance(scrathcing resistance).
[0022] Examples of derivatives of 4,4'-diaminodiphenylmethane are
3,3'-dichloro-4,4'-diaminodiphenylmethane,
3,3'-dimethyl-5,5'-diethyl-4,4- '-diaminodiphenylmethane,
3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethan- e,
3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane,
3,3',5,5'-tetraisopropyl-4,4'-diaminodiphenylmethane,
3,3'-dimethyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane,
3,3'-diethyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane,
3,3'-dimethyl-5,5'-di-t-butyl-4,4'-diaminodiphenylmethane,
3,3'-dichloro-5,5'-diethyl-4,4'-diaminodiphenylmethane,
2,2'-dichloro-3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane, and
2,2',3,3'-tetrachloro-4,4'-diaminodiphenylmethane. Among them,
2,2'-dichloro-3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane is
particularly preferable because its toxicity is relative low.
[0023] Though the blending ratio between the amount of the
isocyanate group-terminated urethane prepolymer and the amount of
the aromatic polyamine compound contained in the urethane cover
composition is not particularly limited, they are preferably mixed
so that the molar ratio of the amino group to the isocyanate group
(NH.sub.2/NCO) falls within the range of from 0.7 to 1.2,
preferably from 0.8 to 1.05, more preferably from 0.85 to 1.0. If
the ratio is adjusted so that a cured product of the resulting
polyurethane composition has buret crosslinking or allophanate
crosslinking, a polyurethane cover to be formed from the cured
product has a three-dimensionally crosslinked structure, and hence
is excellent in durability and abrasion resistance.
[0024] The urethane cover composition used in the present invention
may further contain any conventionally catalyst known in a urethane
reaction. Examples of the catalysts are a monoamine such as
triethylamine and N,N-dimethylcyclohexylamine; a polyamine such as
N,N,N',N'-tetramethyleth- ylenediamine and
N,N,N',N",N"-pentamethyldiethylenetriamine; a cyclic diamine such
as 1,8-diazabicyclo[5,4,0]-7-undecene (DBU) and triethylenediamine;
and a tin catalyst such as dibutyltin dilaurylate and dibutyltin
diacetate. Among them, 1,8-diazabicyclo[5,4,0]-7-undecene (DBU) and
triethylenediamine are preferable. In the case that the reactivity
of the isocyanate group is too high, a retarding catalyst may be
used. Examples of the retarding catalyst are organic carboxylic
acids such as acetic acid, azelaic acid, and adipic acid. Among
them, azelaic acid is preferably used.
[0025] As required, the polyurethane cover composition may further
contain a filler such as barium sulfate, a coloring agent such as
titanium dioxide, and other additives such as a dispersant,
antioxidant, ultraviolet absorber, light stabilizer, fluorescent
material, and fluorescent brightener, as long as any desired
property is not deteriorated.
[0026] The preparation of the polyurethane cover composition
preferably needs to mix the isocyanate group-terminated urethane
prepolymer and the aromatic polyamine compound homogeneously. Thus,
the two components are preferably mixed at such a temperature that
the aromatic polyamine compound is in a molten state. For example,
the urethane prepolymer is heated to a temperature close to such a
temperature that the aromatic polyamine compound turned into a
molten state and then mixed with the aromatic polyamine compound in
a molten state.
[0027] With respect to the polyurethane cover of the golf ball of
the present invention, the hardness of the cured product of the
foregoing polyurethane cover composition (the hardness of the cured
product itself may be referred to as "slab hardness") is preferably
not less than 35, more preferably not less than 40 by Shore D
hardness. If the hardness is less than 35 by Shore D, the resulting
cover is so soft that the golf ball with this cover is easy to
spin, exhibits a lowered repulsion property and also exhibits a
lower abrasion resistance (scratching resistance) against the shot
by an iron or a sand wedge. Since the cover becomes harder as the
Shore D hardness (slab hardness) of the cured product increases,
the cover having too high a hardness results in a golf ball which
imparts a hard shot feeling to the golfer and which cannot ensure
satisfactory controllability in approach shots because of too low
spin rate. Therefore, the Shore D hardness of the cured product
forming the polyurethane cover is preferably not more than 55, more
preferably not more than 52. The polyurethane cover preferably has
the thickness of from 0.7 mm to 1.3 mm.
[0028] The intermediate layer of the solid golf ball of the present
invention is formed from a material having a flexural modulus of
from 150 MPa, preferably from 200 MPa, to 420 MPa, preferably to
400 MPa. The flexural modulus of the intermediate layer is
indicating the elasticity of the material forming the intermediate
layer and is a factor particularly influencing the flight distance
of the golf ball. If the intermediate layer has the flexural
modulus of lower than 150 MPa, the resulting golf ball exhibits a
lowered repulsion property and hence offers a shorter flight
distance. On the other hand, if the intermediate layer has the
flexural modulus of higher than 420 MPa, the resulting golf ball is
so hard that it imparts an inferior shot feeling to the golfer. In
the present invention, the flexural modulus is therefore adjusted
to fall within the aforementioned range, in view of that the
flexural modulus of the intermediate layer reflects the behavior of
the deformation of the golf ball that will occur upon shot. If the
flexural modulus of the intermediate layer is so adjusted, the
intermediate layer, for example, has a Shore D hardness of not less
than 55, preferably not less than 60, and has a Shore D hardness
not more than 70, preferably not more than 68. If the Shore D
hardness of the intermediate layer is less than 55, the
intermediate layer is so soft that the resulting golf ball exhibits
a lowered repulsion property, while if it is more than 70, the
intermediate layer is so hard that the resulting golf ball tends to
impart a poor shot feeling to the golfer.
[0029] The material forming the intermediate layer is not
particularly limited so long as the flexural modulus thereof falls
within the aforementioned range. Examples of the materials are a
thermoplastic resin such as a polyurethane resin, an ionomer resin,
nylon, and polyethylene; and a thermoplastic elastomer such as a
polystyrene elastomer, a polyolefin elastomer, a polyurethane
elastomer, and a polyester elastomer. Among them, the ionomer resin
is particularly preferable in view of its superior repulsion
property and durability. Examples of the ionomer resin are one
prepared by neutralizing at least a part of carboxyl groups in a
copolymer of ethylene and .alpha.,.beta.-unsaturated carboxylic
acid with a metal ion, and one prepared by neutralizing at least a
part of carboxyl groups in a terpolymer of ethylene,
.alpha.,.beta.-unsaturated carboxylic acid and
.alpha.,.beta.-unsaturated carboxylic acid ester with a metal ion.
Examples of the .alpha.,.beta.-unsaturated carboxylic acids are
acrylic acid, methacrylic acid, fumaric acid, maleic acid, and
crotonic acid. Among them, acrylic acid and methacrylic acid are
particularly preferable. Examples of the .alpha.,.beta.-unsaturated
carboxylic acid esters are methyl ester, ethyl ester, propyl ester,
n-butyl ester, isobutyl ester and the like of acrylic acid,
methacrylic acid, fumaric acid, maleic acid and the like. Among
them, acrylic ester and methacrylic ester are particularly
preferable. The metal ion for neutralizing the carboxylic group
includes sodium ion, potassium ion, lithium ion, magnesium ion,
calcium ion, zinc ion, barium ion, aluminum ion, tin ion, zirconium
ion, and cadmium ion. Among them, sodium ion, zinc ion and
magnesium ion are preferable in view of improving the repulsion
property and durability. In the present invention, the acid value
and the metal ion content of the ionomer resin are not particularly
limited. Further, it is possible to use a single or a mixture of
plural ionomer resins so that the flexural modulus of the resulting
intermediate layer falls within the aforementioned range.
[0030] The intermediate layer may further contain a specific
gravity adjusting agent such as barium sulfate or tungsten. In the
case that the intermediate layer contains a filler, it is
preferable to adjust the flexural modulus of the intermediate layer
containing the filler so as to fall within the aforementioned
range. The intermediate layer according to the present invention
has a thickness of from 0.5 mm to 1.5 mm, preferably from 0.7 mm to
1.2 mm. If the thickness of the intermediate layer is less than 0.5
mm, the resulting golf ball has a lowered repulsion property, while
if it is more than 1.5 mm, the resulting golf ball imparts a hard
shot feeling to the golfer and has a lowered repulsion
property.
[0031] The solid center of the solid golf ball according to the
present invention has an outer diameter of from 36.7 mm to 40.8 mm,
preferably from 38.0 mm to 40.0 mm. If the outer diameter of the
center is less than 36.7 mm, either of the intermediate layer and
the polyurethane cover becomes so thick as to cause the lowered
repulsion property and a poor shot feeling. On the other hand, if
the outer diameter of the center is more than 40.8 mm, the
intermediate layer and the polyurethane cover become so thin that
the resulting golf ball cannot enjoy the effects which would
otherwise be provided by the intermediate layer and the
polyurethane cover. There is no particular limitation on the
composition of the solid center, as long as its outer diameter is
within the range described above. Usually, the solid center is a
vulcanized body of a rubber composition, which is generally used
for the centers of solid golf balls. The rubber composition for the
solid center (hereinafter referred to as "center rubber
composition" as the case may be) preferably comprises a base
rubber, an organic peroxide as a crosslinking agent, an organic
sulfur compound, and a co-crosslinking agent. As required, the
center rubber composition may further contain additives such as a
specific gravity adjusting agent, antioxidant, and color powder.
Examples of the base rubbers are butadiene rubber (BR),
ethylene-propylene-diene terpolymer (EPDM), isoprene rubber (IR),
styrene-butadiene rubber (SBR), and acrylonitrile-butadiene rubber
(NBR). Among them, butadiene rubber, particularly
cis-1,4-polybutadiene, is preferable in view of its superior
repulsion property. A preferred embodiment of the present invention
employs a high-cis polybutadiene rubber having cis-1,4 bonds in a
proportion of not less than 40%, preferably not less than 70%, more
preferably not less than 90%.
[0032] Examples of the organic peroxides for use in the present
invention are dicumyl peroxide,
1,1-bis(t-butylperoxy)-3,5-trimethylcyclohexane,
2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide.
Among them, dicumyl peroxide is preferable. The amount of the
organic peroxide to be blended in the center rubber composition is
preferably from 0.1 to 3.0 parts by mass, more preferably from 0.2
to 2.0 parts by mass based on 100 parts by mass of the base
rubber.
[0033] The co-crosslinking agent used in the present invention
includes, for example, an .alpha.,.beta.-unsaturated carboxylic
acid or a metal salt thereof. Typically preferred is
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms such as acrylic acid and methacrylic acid. As a metal forming
metal salts of the .alpha.,.beta.-unsaturated carboxylic acid,
monovalent or divalent metals such as zinc and magnesium is
preferably used. Among them, zinc acrylate is preferable because it
can impart the higher repulsion property to the golf ball. The
amount of the co-crosslinking agent to be blended in the center
rubber composition is preferably from 15 to 50 parts by mass, more
preferably 20 to 40 parts by mass based on 100 parts by mass of the
base rubber.
[0034] The center rubber composition used in the present invention
preferably further contains an organic sulfur compound (diphenyl
disulfide derivative) represented by the following formula: 1
[0035] wherein each of X.sup.1 to X.sup.10 is any one selected from
the group consisting of a hydrogen atom, a chlorine atom, a bromine
atom, an iodine atom, and a cyano group, and X.sup.1 to X.sup.10
may be same or different each other. Although the diphenyl
disulfide derivative can have a symmetric or asymmetric structure,
it is preferable that the diphenyl disulfide derivative has the
symmetric structure (bis-structure). Examples of the diphenyl
disulfide derivatives are diphenyl disulfide; mono-substituted
diphenyl disulfide such as bis(4-chlorophenyl) disulfide,
bis(3-chlorophenyl) disulfide, bis(4-bromophenyl) disulfide,
bis(3-bromophenyl) disulfide, bis(4-fluorophenyl) disulfide,
bis(4-iodophenyl) disulfide, and bis(4-cyanophenyl) disulfide;
di-substituted diphenyl disulfide such as bis(2,5-dichlorophenyl)
disulfide, bis(3,5-dichlorophenyl) disulfide,
bis(2,6-dichlorophenyl) disulfide, bis(2,5-dibromophenyl)
disulfide, bis(3,5-dibromophenyl) disulfide,
bis(2-chloro-5-bromophenyl) disulfide, and
bis(2-cyano-5-bromophenyl) disulfide; tri-substituted diphenyl
disulfides such as bis(2,4,6-trichlorophenyl) disulfide and
bis(2-cyano-4-chloro-6-b- romophenyl) disulfide; tetra-substituted
diphenyl disulfide such as bis(2,3,5,6-tetrachlorophenyl)
disulfide; and penta-substituted diphenyl disulfide such as
bis(2,3,4,5,6-pentachlorophenyl) disulfide and
bis(2,3,4,5,6-pentabromophenyl) disulfide. These diphenyl
disulfides can exert some influence upon the vulcanized state of
the vulcanized rubber to enhance the repulsion property of the
resulting golf ball. Among them, diphenyl disulfide and
bis(pentachlorophenyl) disulfide are particularly preferable from
the viewpoint that they can impart the higher repulsion property to
the golf ball.
[0036] The conditions for vulcanizing the center rubber composition
can be established appropriately depending upon the formulation of
the rubber composition. It is desirable that the center rubber
composition is vulcanized for 10 to 60 minutes at the temperature
of not lower than 130.degree. C., more preferably not lower than
160.degree. C., and not higher than 200.degree. C., more preferably
not higher than 180.degree. C. According to another preferred
embodiment of the present invention, the center rubber composition
is vulcanized by heating at a relatively low temperature ranging
between 130.degree. C. and 150.degree. C. for 20 to 40 minutes and
then at a higher temperature ranging between 160.degree. C. and
180.degree. C. for 5 to 15 minutes. The two-step vulcanization
provides a center having uniform hardness between the surface
portion and the internal portion of the solid center.
[0037] The solid center preferably has the deformation amount of
not less than 2.8 mm, more preferably not less than 2.85 mm, and
not more than 3.5 mm, more preferably not more than 3.3 mm, when
applying a load from 98N (10 kgf) as an initial load to 1275N (130
kgf) as a final load. If the deformation amount is less than 2.8
mm, the center becomes so hard that the center greatly influences
the shot feeling, thus resulting in a larger impact given to the
golfer upon shot (that is, a harder shot feeling imparted to the
golfer). On the other hand, if the deformation amount is more than
3.5 mm, the center becomes so soft that the resulting golf ball
cannot provide a satisfactory flight distance.
[0038] The solid golf ball of the present invention preferably has
the deformation amount of not less than 2.7 mm, more preferably not
less than 2.8 mm, and not more than 3.5 mm, more preferably not
more than 3.3 mm, when applying a load from 98N (10 kgf) as an
initial load to 1275N (130 kgf) as a final load. If the deformation
amount is less than 2.7 mm, the golf ball imparts a harder shot
feeling to the golfer, while if the deformation amount is more than
3.5 mm, the golf ball has a lowered repulsion property and hence
cannot exhibit a satisfactory flight distance.
[0039] The solid golf ball of the present invention can be
manufactured by a well-known process which is conventionally
employed for manufacturing the golf ball having a polyurethane
cover. For example, the solid center of vulcanizing-molded body is
covered with the intermediate layer to form a solid core. In
covering the solid center with the intermediate layer, it is
possible to employ a process including: forming the intermediate
layer material into two hemispherical half shells; enveloping the
solid center with the two half shells; and then pressure-molding.
Alternatively, it is possible to employ a process including
injection-molding the intermediate layer material directly onto the
solid center to cover the solid center. Subsequently, the obtained
solid core is hold in the hemispherical mold, and then the
polyurethane cover composition is charged into the hemispherical
mold. The hemispherical mold holding the solid core is inverted to
mate with another hemispherical mold into which the polyurethane
cover composition has been charged. Finally, the polyurethane cover
composition is cured to mold the cover. The curing reaction of the
polyurethane cover composition is preferably conducted at the
temperature of from 30.degree. C. to 120.degree. C. for 2 to 60
minutes, preferably at the temperature of from 50.degree. C. to
80.degree. C. for 5 to 30 minutes. As required, the polyurethane
cover is formed with a multiplicity of dimples at the surface
thereof during molding the cover. Further, the golf ball of the
present invention is usually provided with paint finish, a marking
stamp and the like to enhance the appearance and the commercial
value thereof before it is launched into the market.
[0040] In the present invention, the polyurethane cover may be
composed of a single layer or plural layers.
EXAMPLES
[0041] The following examples illustrate the present invention,
however these examples are intended to illustrate the invention and
are not to be construed to limit the scope of the invention. Many
variations and modifications of such examples will exist without
departing from the scope of the inventions. Such variations and
modifications are intended to be within the scope of the
invention.
[0042] [Measurement and Evaluation Methods]
[0043] 1. Compressive Deformation Amount (mm)
[0044] The deformation amount (the deformation amount of shrinkage
along the loading direction) was measured when applying a load from
98N as an initial load to 98 N as a final load of 1275 N in terms
of each of the solid center and the solid golf ball.
[0045] 2. Repulsion Coefficient
[0046] An aluminum cylindrical body having a weight of 198.4 g was
allowed to collide with each solid golf ball at the speed of 45
m/sec. The respective speeds of the cylindrical body and the solid
golf ball before and after the collision were measured, and the
repulsion coefficient of each solid golf ball was calculated from
the respective speeds thus measured and the respective masses of
the cylindrical body and the solid golf ball. For each solid golf
ball, 12 samples were measured. The average of the measured values
was regarded as the repulsion coefficient of each solid golf ball.
The repulsion coefficient of each solid golf ball was represented
as an index relative to 100 representing the repulsion coefficient
of the golf ball No. 12.
[0047] 3. Flight Distance (Carry) and Spin Rate(rpm)
[0048] Each golf ball was hit with a titan-head wood driver (W#1)
attached to a swing robot manufactured by TRUETEMPER CO. at the
head speed of 45 m/sec. The flight distance from the hitting point
to the point at which the ball fell to the ground, was measured.
The spin rate was determined by hitting each golf ball with a sand
wedge attached to the swing robot at the head speed of 20
m/sec.
[0049] 4. Shot Feeling
[0050] An actual hitting test was carried out by ten golfers
including professional golfers and high-level amateur golfers with
a W#1 club. The shot feeling of each golf ball was evaluated based
on the magnitude of the impact upon shot according to the following
rating criteria. The rating category to which the largest number of
golfers agreed for each golf ball was determined as the shot
feeling of the golf ball.
[0051] Rating Criteria:
[0052] "Excellent": A golf ball gave a very small impact upon shot
and imparted a very soft shot feeling;
[0053] "Good": A golf ball gave a small impact upon shot and
imparted a soft shot feeling;
[0054] "Fair": A golf ball gave an ordinary impact upon shot;
and
[0055] "Poor": A golf ball gave a large impact upon shot, hence
imparted a poor shot feeling.
[0056] 5. Flexural Modulus
[0057] According to JIS-K7171, a 4 mm-thick, 20 mm-long and 10
mm-wide plate formed from each intermediate layer composition was
subjected to a three-point flexural test. The flexural modulus of
each plate was determined from stresses corresponding to strain
.epsilon..sub.1=0.0005 and strain .epsilon..sub.2=0.0025.
[0058] 6. Hardness of the Cured Product of Polyurethane Cover
Composition (Slab Hardness)
[0059] Each polyurethane cover composition was formed into sheets
each having a thickness of about 2 mm by hot press molding and the
resulting sheets were conserved at 23.degree. C. for two weeks. At
least three of the sheets were stacked one upon another to remove
the influence of the measuring substrate on which the sheets were
placed, and the stack was subjected to the measurement using a
spring-type Shore D hardness tester prescribed by ASTM-D2240.
[0060] 7. Abrasion Resistance (Scratching Resistance)
[0061] Two portions of each golf ball were each hit once using a
commercially available pitching wedge attached to the swing robot
at the head speed of 36 m/sec. The condition of each of the two
portions thus hit was visually observed and rated on five levels
according to the following criteria. The worse result of the two
portions was regarded as the result of the golf ball.
[0062] Rating Criteria:
[0063] "Good": The surface of the golf ball had few flaws, which
were at an unnoticeable degree;
[0064] "Fair": The surface of the golf ball had clearly noticeable
flaws and slight nap; and
[0065] "Poor": The surface of the golf ball was considerably shaved
and conspicuously napped.
[0066] [Manufacture of Golf Ball]
[0067] Solid center rubber compositions of the formulation shown in
Table 1 were each subjected to vulcanization at 160.degree. C. for
30 minutes to form ten types of solid centers S1 to S10.
1TABLE 1 Type of Solid Center Composition S1 S2 S3 S4 S5 S6 S7 S8
S9 S10 BR18 100 100 100 100 100 100 100 100 100 100 Zinc acrylate
33 33 33 33 33 33 33 33 33 33 Zinc oxide 14.8 14.2 16.6 16.6 16.6
16.6 16.6 16.7 13.4 19.6 Diphenyl disulfide 0.5 0.5 0.5 0.3 1 -- --
-- 0.5 0.5 Bis(pentachlorophenyl) -- -- -- -- -- 0.5 -- -- -- --
disulfide Dibenzyl disulfide -- -- -- -- -- -- 0.5 -- -- -- Dicumyl
peroxide 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Unit: Parts by
mass
[0068] BR18: high cis-1,4-polybutadiene produced by JSR CO.
[0069] Each of the solid centers thus formed was subjected to the
injection-mold using each of the intermediate layer materials shown
in Table 2 in order to form a solid core comprising the solid
center coated with the intermediate layer.
2TABLE 2 Material of Flexural Intermediate Layer modulus Type
Commercial name (MPa) Note M 1 HIMILAN 1605 370 Mitsui-Dupont
Polychemical CO., M 2 HIMILAN 1555 250 Mitsui-Dupont Polychemical
CO., M 3 HIMILAN 1856 70 Mitsui-Dupont Polychemical CO., M 4 SURLYN
8140 490 Dupont CO. Note on TABLE 2: Each of the intermediate layer
materials is an ethylene/methacrylic acid ionomer resin of the type
neutralized with Na.
[0070] Each of the solid cores thus formed was held in a
hemispherical mold having a dimple pattern, and each of four types
of polyurethane cover materials C1 to C4 shown in Table 3 was
injected into the mold. Subsequently, the mold was inverted and
mated with another hemispherical mold having a dimple pattern into
which the same type of polyurethane cover material had been
injected, and curing reaction of the cover material was conducted
to form a polyurethane cover.
3TABLE 3 Cover composition C1 C2 C3 C4 C5 C6 Isocyanate group
terminated urethane prepolymer Adiprene LF800A -- -- 100 -- -- --
Adiprene LF900A -- 100 -- -- -- -- Adiprene LF950A 100 -- -- -- --
-- Adiprene LF600D -- -- -- 100 -- -- Aromatic polyamine compound
Lonzacure M-CDEA 26.1 16.2 12.4 31.2 -- -- Thermoplastic urethane
resin Pandex T1198 -- -- -- -- 100 -- Ionomer resin SURLYN 8120 --
-- -- -- -- 50 HIMILAN 1855 -- -- -- -- -- 50 Filler (Titanium
dioxide) 2 2 2 2 2 2 Slab Hardness (Shore D) 54 40 33 62 53 50
formulation: parts by mass
[0071] Note on table 3:
[0072] ADIPRENE LF800A: a TDI/PTMG type prepolymer produced by
UNIROYAL CO., LTD., NCO content=2.9%, residual tolylene
diisocyanate content=not more than 0.1%.
[0073] ADIPRENE LF900A: a TDI/PTMG type prepolymer produced by
UNIROYAL CO., LTD., NCO content=3.8%, residual tolylene
diisocyanate content=not more than 0.1%.
[0074] ADIPRENE LF950A: a TDI/PTMG type prepolymer produced by
UNIROYAL CO., LTD., NCO content=6.1%, residual tolylene
diisocyanate content=not more than 0.1%.
[0075] ADIPRENE LF600D: a TDI/PTMG type prepolymer produced by
UNIROYAL CO., LTD., NCO content=7.3%, residual tolylene
diisocyanate content=not more than 0.1%;
[0076] LONZACURE M-CDEA:
2,2'-dichloro-3,3',5,5'-tetraethyl-4,4'-diaminodi- phenylmethane,
produced by LONZA CO.
[0077] PANDEX T1198: a thermoplastic polyurethane elastomer;
[0078] SURLYN 8120: a Na-neutralized ethylene/methacrylic acid
ionomer produced by DUPONT CO.
[0079] HIMILAN 1855: a Zn-neutralized ethylene/methacrylic acid
ionomer produced by MITSUI-DUPONT POLYCHEMICAL.
[0080] In the cases that thermoplastic urethane resin C5 and
ionomer resin C6 were used as cover materials, each cover was
formed by injection-molding. Each of resulting golf balls was
removed from the mold, deburred, and coated with a white paint and
then with a clear paint to give a solid golf ball having a diameter
of 42.8 mm and a mass of 45.2 to 45.7 g. These solid golf balls
were evaluated as to their flying performance, shot feeling and the
like. The results of the evaluations are shown in Tables 4 and
5.
4TABLE 4 Golf ball No. 1 2 3 4 5 6 7 8 9 10 Solid Center -- -- --
-- -- -- -- -- -- -- Type S1 S2 S3 S3 S3 S4 S5 S6 S7 S8
Diameter(mm) 39.6 38.8 38.8 38.8 38.8 38.8 38.8 38.8 38.8 38.8
Deformation (mm) 3.18 3.17 3.16 3.16 3.16 3.12 3.24 3.19 3.09 3.1
Intermediate Layer -- -- -- -- -- -- -- -- -- -- Type M1 M1 M2 M1
M1 M1 M1 M1 M1 M1 Flexural Modulus(MPa) 370 370 250 370 370 370 370
370 370 370 Thickness (mm) 0.8 0.8 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2
Shore D hardness 67 67 62 67 67 67 67 67 67 67 Cover -- -- -- -- --
-- -- -- -- -- Type C1 C1 C1 C1 C2 C1 C1 C1 C1 C1 Thickness (mm)
0.8 1.2 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Slab hardness( Shore D) 54
54 54 54 40 54 54 54 54 54 Properties of golf ball -- -- -- -- --
-- -- -- -- -- Deformation (mm) 3.06 3.08 3.06 2.98 3.1 2.96 3.09
3.03 2.94 2.95 Repulsion coefficient 108 107 107 109 107 107 108
110 104 105 Flight distance(yard) 235 233 233 236 233 233 235 237
228 230 Spin rate (rpm, with SW) 7000 7000 7100 7000 7200 7000 7000
7000 7000 7000 Shot feeling E E E E E E E E G G Scrathcing
resistance G G G G G G G G G G E: Excellent, G: Good
[0081] Golf balls Nos. 1 to 10 are golf balls satisfying the
requirements of the present invention as to the outer diameter of
the solid center, the thickness and flexural modulus of the
intermediate layer, and the composition, thickness and Shore D
hardness of the polyurethane cover. Every golf ball was found to
exhibit a high repulsion coefficient and to be excellent in flight
distance with a wood (W#1), the spin rate with a sand wedge, and
the shot feeling. Golf balls Nos. 1 to 8 each employing a diphenyl
disulfide type organic sulfur compound as a vulcanizing agent for
the solid center rubber composition were each found to exhibit a
higher repulsion property and a longer flight distance than both of
golf ball No. 9 employing dibenzyl disulfide and golf ball No. 10
not employing any organic sulfur compound (sulfide compound). Golf
ball No. 8 employing bis(pentachlorophenyl) disulfide as an organic
sulfur compound was found to exhibit a particularly high repulsion
property and a very long flight distance. As can be understood from
these results, if diphenyl disulfide type organic sulfur compound
is used for the center rubber composition, a golf ball exhibiting a
high repulsion property and a long flight distance is obtained.
5TABLE 5 Golf ball No. 11 12 13 14 15 16 17 18 Solid Center -- --
-- -- -- -- -- -- Type S9 S3 S3 S3 S3 S3 S3 S10 Diameter (mm) 37.6
38.8 38.8 38.8 38.8 38.8 38.8 37.6 Deformation (mm) 3.15 3.16 3.16
3.16 3.16 3.16 3.16 3.12 Intermediate Layer -- -- -- -- -- -- -- --
Type M1 M3 M4 M1 M1 M1 M1 M1 Flexural Modulus(MPa) 370 70 490 370
370 370 370 370 Thickness (mm) 0.8 1.2 1.2 1.2 1.2 1.2 1.2 1.8
Shore D hardness 67 58 70 67 67 67 67 67 Cover -- -- -- -- -- -- --
-- Type C1 C1 C1 C3 C4 C5 C6 C1 Thickness (mm) 1.8 0.8 0.8 0.8 0.8
0.8 0.8 0.8 Slab hardness( Shore D) 54 54 54 33 62 53 50 54
Properties of golf ball -- -- -- -- -- -- -- -- Deformation (mm)
3.12 3.14 2.85 3.19 2.82 2.99 3.01 2.77 Repulsion coefficient 101
100 111 101 110 104 103 107 Flight distance (yard) 219 222 236 217
236 226 224 232 Spin rate (rpm, with SW) 6900 7300 6800 7400 6200
6700 6400 6800 Shot feeling Fair Poor Poor Poor Poor Fair Fair Poor
Scratching resistance Good Fair Poor Fair Poor Poor Poor Good
[0082] Golf ball No. 11 exhibited a lower repulsion property and a
shorter flight distance because the thickness of the polyurethane
cover was as too large as 1.8 mm. Golf ball No. 12 was too soft and
hence exhibited a lower repulsion property and a shorter flight
distance, and also imparted an inferior shot feeling because the
material used for the intermediate layer had the flexural modulus
of 70 MPa. Golf ball No. 13 was the case that a material having a
flexural modulus of 490 MPa is used for the intermediate layer.
Although this golf ball exhibited a higher repulsion property and a
longer flight distance, it imparted a harder shot feeling (inferior
shot feeling) to the golfer due to the excessively hard
intermediate layer.
[0083] These results indicated that use of the material having the
flexural modulus of from 150 to 420 MPa for the intermediate layer
was preferable for making the shot feeling and the repulsion
coefficient well-balanced and compatible with each other. Golf ball
No. 14 of which the polyurethane cover had a slab hardness (Shore D
hardness) of 33 imparted an inferior shot feeling to the golfer.
Further, golf ball No. 14 exhibited a shorter flight distance
because the polyurethane cover was so soft that its repulsion
property was lowered. The golf ball No. 15 was the case that the
polyurethane cover had a slab hardness (Shore D hardness) of 62. In
this case, the cover was so hard that the golf ball imparted a poor
shot feeling to the golfer. Further, the spin rate of golf ball No.
15 hit with a sand wedge was reduced because, conceivably, the
cover was easy to slip. Golf balls Nos. 16 and 17 employed a
thermoplastic urethane resin and an ionomer resin, respectively, as
their cover materials. The both golf balls Nos. 16 and 17 did not
have the polyurethane cover with the repulsion coefficient as high
as the polyurethane cover used in the present invention, and hence
exhibited a reduced flight distance. Golf ball No. 18 was the case
that the intermediate layer had a thickness of 1.8 mm. In this
case, the intermediate layer was so thick that the golf ball
imparted a harder shot feeling (or an inferior shot feeling).
[0084] The solid golf ball of the present invention comprises the
solid center, the intermediate layer, and the cured polyurethane
cover, and is characterized in that: the polyurethane cover has a
thickness of from 0.5 to 1.5 mm and a Shore D hardness of from 35
to 55; and the intermediate layer has a thickness of from 0.5 to
1.5 mm and is formed from a material having a flexural modulus of
from 150 to 420 MPa. The golf ball thus constructed offers a shot
feeling and a flight distance that are balanced well. If the golf
ball employs a solid center formed by vulcanizing a center rubber
composition containing a diphenyl disulfide, the golf ball can have
a further enhanced repulsion property and exhibit a longer flight
distance.
[0085] Since the polyurethane cover of the solid golf ball
according to the present invention is formed from a polyurethane
having a three-dimensionally crosslinked structure such as buret
crosslinking or allophanate crosslinking, the polyurethane cover is
excellent in durability and abrasion resistance. Particularly, by
the use of an isocyanate group-terminated urethane prepolymer
having a residual isocyanate monomer content of not more than 0.5%
in forming the polyurethane cover, the curing reaction of the
polyurethane is allowed to proceed uniformly, and hence it is
possible to further enhance the abrasion resistance and durability
of the cover. This application is based on Japanese Patent
application No.2001-294466 filed on Sep. 26, 2001, the contents of
which are hereby incorporated by reference.
* * * * *