U.S. patent application number 10/387484 was filed with the patent office on 2003-09-18 for golf ball.
Invention is credited to Mano, Satoshi.
Application Number | 20030176242 10/387484 |
Document ID | / |
Family ID | 28035046 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030176242 |
Kind Code |
A1 |
Mano, Satoshi |
September 18, 2003 |
Golf ball
Abstract
A golf ball which improves adherence of a coating to a cover and
which improves spin retention without sacrificing the other
properties of the coating. The golf ball has a core, a cover of at
least one layer covering the core and a coating formed on an outer
surface of the cover, wherein a thickness of the coating is 25 to
125 .mu.m, a 50%-modulus of the coating is 5 to 50 MPa, and a value
R expressed by R=PL/CL/1000 is 0.01 to 0.5, where CL (mm)
represents a thickness of an outermost layer of the cover and PL
(.mu.m) represents a thickness of the coating.
Inventors: |
Mano, Satoshi; (Kobe-shi,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
28035046 |
Appl. No.: |
10/387484 |
Filed: |
March 14, 2003 |
Current U.S.
Class: |
473/378 |
Current CPC
Class: |
A63B 37/0003 20130101;
A63B 37/00221 20200801; A63B 37/12 20130101; A63B 37/0033 20130101;
A63B 37/0064 20130101; A63B 37/008 20130101; A63B 37/0037 20130101;
A63B 37/0096 20130101; A63B 37/00222 20200801; A63B 37/0074
20130101 |
Class at
Publication: |
473/378 |
International
Class: |
A63B 037/12 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2002 |
JP |
2002-070257 |
Claims
What is claimed is:
1. A golf ball having a core, a cover of at least one layer
covering the core and a coating formed on an outer surface of the
cover, wherein a thickness of said coating is 25 to 125 .mu.m, a
50%-modulus of the coating is 5 to 50 MPa, and a value R expressed
by an equation (1) is 0.01 to 0.5: R=PL/CL/1000 (1) where CL (mm)
represents a thickness of an outermost layer of the cover and PL
(.mu.m) represents a thickness of said coating.
2. The golf ball according to claim 1, wherein the outermost layer
of the cover has thickness CL (mm) of 0.5 to 2.5.
3. The golf ball according to claim 1, wherein the coating is
formed with polyurethane paint including polyol and
polyisocyanate.
4. The golf ball according to claim 3, wherein an equivalent ratio
of trifunctional polyol to bifunctional polyol included in polyol
(trifunctional polyolibifunctional polyol) is 1.0-2.5.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a golf ball having a high
spin retention, that is, a high ratio of a spin rate under a wet
condition to a spin rate under a dry condition.
[0003] 2. Description of the Background Art
[0004] A surface of a golf ball is generally covered with a coating
to give a gloss in appearance. As a golf ball is used in a severe
environment, it is very difficult to retain a glossy appearance for
a long period, and demanded levels of various properties of the
coating are inevitably high. Some of the properties demanded for
the coating are, for example, flexibility to prevent cracking even
when the ball is deformed to a large extent by hitting with a
driver or the like, abrasion resistance to prevent damage by large
friction caused by an iron shot, wear resistance for a bunker shot,
and durability to prevent peeling of the coating by hitting with
various clubs or by using the ball in a rainy day.
[0005] In Japanese Patent Laying-Open No. 2001-17574, for example,
the abrasion resistance is improved by setting tensile strength of
a cover material and a coating to approximate values to enhance
adherence of the coating to the cover. In Japanese Patent
Laying-Open No. 2000-176047, in addition, the abrasion resistance
and wear resistance are enhanced by making a thickness of a coating
as small as 5-20 .mu.m.
[0006] Conventionally, golf balls with balata covers are generally
and widely used by low handicap and professional golfers by virtue
of their superior hit feeling and controllability. Recently,
various soft covers have been proposed to replace the balata
covers, however, because of their complicated fabrication process
and poor cut resistance.
[0007] In a golf ball having improved controllability proposed in
Japanese Patent Laying-Open No. 10-179802, a basic resin of a cover
is formed having as a main component a heated mixture of two
components, that is, an ionomer resin and a
styrene-butadiene-styrene block copolymer including a polybutadiene
block containing an epoxy group or a styrene-isoprene-styrene block
copolymer including a polyisoprene block containing an epoxy group.
A composition for the cover has a flexural modulus of 50-300 MPa
and a Shore D hardness of 40-60.
[0008] In a golf ball having improved controllability proposed in
GB 2311530, a basic resin of a cover is formed having as a main
component a heated mixture of three components, that is, an ionomer
resin, an acid-modified thermoplastic elastomer or a thermoplastic
elastomer having an OH group at the end of the polymer chain, and a
styrene-butadiene-styrene block copolymer including a polybutadiene
block containing an epoxy group or a styrene-isoprene-styrene block
copolymer including a polyisoprene block containing an epoxy group.
A composition for the cover has a flexural modulus of 50-300 MPa
and a Shore D hardness of 40-60.
[0009] In Japanese Patent Laying-Open No. 2001-137386, in addition,
a golf ball having a high spin retention, that is, a high ratio of
a spin rate under a wet condition to a spin rate under a dry
condition is proposed, wherein a loss tangent (tan.delta.) at
-10.degree. C. in dynamic viscoelasticity of a cover material is
set to 0.15-0.70.
[0010] All of these prior arts improve the spin retention in terms
of a cover material, not in terms of a coating of a golf ball.
SUMMARY OF THE INVENTION
[0011] The present invention provides a golf ball which improves
adherence of a coating to a cover by respectively setting a
thickness of the coating, a 50%-modulus and a ratio of a thickness
of the cover to that of the coating of the golf ball to certain
ranges, and which improves a spin retention without sacrificing
needed properties of the coating.
[0012] A golf ball according to the present invention has a core, a
cover of at least one layer covering the core and a coating formed
on an outer surface of the cover, wherein a thickness of the
coating is 25 to 125 .mu.m, a 50%-modulus of the coating is 5 to 50
MPa, and a value R expressed by the following equation (1) is 0.01
to 0.5:
R=PL/CL/1000 (1)
[0013] where CL (mm) represents a thickness of an outermost layer
of the cover and PL (.mu.m) represents a thickness of the
coating.
[0014] The coating is preferably formed with polyurethane paint
including polyol and polyisocyanate. In addition, it is more
preferable that an equivalent ratio of trifunctional polyol to
bifunctional polyol included in the aforementioned polyol
(trifunctional polyol/bifunctional polyol) is 1.0-2.5. In the
present invention, when the cover is formed with a plurality of
layers, the outermost layer of the cover preferably has thickness
CL (mm) of 0.5 to 2.5.
[0015] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0016] A golf ball according to the present invention is
characterized in that, a thickness of a coating is 25 to 125 .mu.m,
a 50%-modulus of the coating is 5 to 50 MPa, and a value R
expressed by the following equation (1) is 0.01 to 0.5:
R=PL/CL/1000 (1)
[0017] where CL (mm) represents a thickness of an outermost layer
of the cover and PL (.mu.m) represents a thickness of the
coating.
[0018] One of the most important properties of the coating is
peeling resistance, that is, a property of the coating of not
peeling off a cover. A golf ball is subject to substantial
deformation due to an external force applied by hitting with a golf
club. When a golfer hits a golf ball with a head speed of about
35-50 m/sec, for example, a body of the golf ball (portions other
than a golf ball coating) deforms by about 40%. Therefore, if
adherence of the coating to the golf ball body is insufficient or
the coating is too hard and elasticity thereof is insufficient, the
coating cannot follow the deformation of the ball body, which
results in cracking of the coating or peeling of the coating away
from the cover.
[0019] The peeling resistance of the coating is becoming especially
important in recent years where a solid golf ball using a cover
including an ionomer resin as a base material is becoming
mainstream. This is because, as the cover made of the ionomer resin
has high strength and breaking of the cover rarely occurs, a
lifetime of the golf ball is determined by peeling of the coating
away from the cover.
[0020] As a result of the research by the inventors on a relation
between the peeling resistance and the thickness and 50%-modulus of
the coating, it is shown that the thicker the coating is, the less
probable the peeling of the coating becomes. That is, as the
coating becomes thicker, a ratio of the thickness of the coating to
the amount of deformation of the golf ball increases, and the
peeling of the coating becomes less probable. In addition, we found
that the spin retention becomes higher by setting the ratio (R) of
the thickness of the coating (PL) to the thickness of the outermost
layer of the cover (CL) to 0.01 to 0.5, and setting the 50% modulus
of the coating to 5-50 MPa.
[0021] <Coating>
[0022] The golf ball according to the present invention is
characterized in that, the thickness of the coating covering the
outermost layer of the cover (PL) is 25 .mu.m to 125 .mu.m. In a
conventional golf ball, a coating as thin as 15-30 .mu.m is used.
According to the present invention, the peeling resistance can be
improved by making the thickness of the coating (PL) larger so that
the coating can follow the deformation of the golf ball at hitting.
It is preferable that the thickness of the coating (PL) is 35-100
.mu.m, especially 40-80 .mu.m. The thickness of the coating is
defined as an average value of the thicknesses at 20 points on a
surface of the golf ball; 10 points on the dimple portions and 10
points on the land portions.
[0023] In the present invention, the 50%-modulus of the coating is
set to 5-50 MPa. If the 50%-modulus is lower than 5 MPa, the
coating of the ball is damaged by friction due to hitting with a
fairway wood or an iron club, and wearing of the coating occurs
with an iron club and sand during a bunker shot. If the 50%-modulus
is higher than 50 MPa, on the other hand, the coating easily cracks
for lack of flexibility, which degrades the appearance. In
addition, the coating peels off the cover due to the cracking of
the coating. The 50%-modulus of the coating is more preferably
10-40 MPa, and further preferably 15-30 MPa. The 50%-modulus of the
conventional coating is about 60 MPa.
[0024] Variety of material, degree of curing, molecular weight and
the like of the paint may be adjusted to set the 50%-modulus of the
coating within the above-mentioned range. Examples of the paint
that can be employed in the present invention include, but are not
limited to, alkyd resin paint, phenol resin paint, amino resin
paint, amino-alkyd resin paint, aminoacrylic resin paint,
unsaturated polyester resin paint, epoxy resin paint, polyurethane
paint, chlorinated rubber paint, acrylic resin paint, vinyl resin
paint, and fluororesin paint. Among these, polyurethane paint can
suitably be used because of its high glossiness and the like.
[0025] Polyurethane paint forms a coating having urethane bonds by
a curing reaction of polyol and polyisocyanate. Examples of
polyisocyanate include aliphatic diisocyanate, alicyclic
diisocyanate, aromatic diisocyanate, and aromatic-aliphatic
diisocyanate such as hexamethylenediisocyanate,
xylylenediisocyanate, hydrogenated xylylenediisocyanate,
isophoronediisocyanate, tetramethyl-xylylenediisocy- anate,
hydrogenated diphenylmethanediisocyanate, and tolylenediisocyanate.
Single polyisocyanate as such may be used, or two or more kinds may
be mixed for use. Among these, aliphatic diisocyanate and alicyclic
diisocyanate can suitably be used because of their high
weatherability and non-yellowing property.
[0026] Diol and triol having low molecular weights and polymer
polyol can be used as the above-mentioned polyol. Examples of the
low molecular weight diol include ethylene glycol, diethylene
glycol, triethylene glycol, butylene glycol, 1,3-butanediol,
1,4-butanediol, neopentyl glycol, and 1,6-hexanediol. Examples of
the low molecular weight triol include glycerine, trimethylol
propane and hexanetriol. Examples of the above-mentioned polymer
polyol include polyether polyol such as polyethylene glycol,
polypropylene glycol and polytetramethylene glycol, polyester
polyol such as polyethylene adipate and poly-.epsilon.-caprolac-
tone, acrylic polyol formed by properly introducing hydroxyl group
into an acrylic polymer, polycarbonate diol synthesized using
cyclic diol, and urethane polyol formed by reacting a diisocyanate
compound with diol and triol to form urethane bonds.
[0027] When the coating is formed using polyurethane paint, the
modulus of the coating can be adjusted with the molecular weight of
the polyol and the number of hydroxyl groups. If the molecular
weight of the polyol is made higher, for example, the modulus of
the coating becomes lower because soft segments increase. If the
molecular weight of the polyol is made lower, on the other hand,
the modulus of the coating becomes higher because soft segments
decrease. If a larger amount of bifunctional diol is included, the
modulus of the coating becomes lower because diol binds to
isocyanate linearly. If a larger amount of trifunctional triol is
included, while the modulus of the coating becomes higher because
triol binds to isocyanate in a three-dimensional manner,
flexibility decreases and cracking or peeling easily occurs. Thus,
the 50%-modulus of the coating can be adjusted to 5-50 MPa by
setting an equivalent ratio of trifunctional polyol to bifunctional
polyol included in the polyol (trifunctional polyol/bifunctional
polyol) to 1.0-2.5.
[0028] In addition, it is preferable that an equivalent ratio of
isocyanate groups in polyisocyanate to hydroxyl groups in polyol
(NCO groups/OH groups) is 0.9-1.5. When the equivalent ratio is
lower than 0.9, the coating will still be sticky after a curing
process, and dusts or contaminants may easily adhere thereto. When
the equivalent ratio is higher than 1.5, on the other hand, some of
the isocyanate groups will remain, which may react with water and
generate CO.sub.2 to cause bubbles within the coating.
[0029] In a composition of the coating according to the present
invention, additives such as a silicon-based slip agent, a leveling
agent, a viscosity adjustment agent, a fluorescent brightening
agent, a blocking inhibitor, a curing catalyst, and a pigment may
be included as needed.
[0030] <Relation Between Thickness of Outermost Layer of Cover
and Thickness of Coating>
[0031] The golf ball according to the present invention is also
characterized in that, a value R expressed by the equation
R=PL/CL/1000 is 0.01-0.5. When the value R is lower than 0.01,
durability of the golf ball decreases. When the value R is higher
than 0.5, on the other hand, a repulsive force of the golf ball
decreases, and thus a carry thereof decreases. It is more
preferable that the value R is 0.0125-0.25. In a conventional golf
ball, the durability is improved by making a coating harder and
thinner, and the value R thereof is 0.002 to less than 0.01.
[0032] Herein, the thickness of the outermost layer of the cover
(CL) is 0.25-2.5 mm, more preferably 0.5-2.0 mm. When the thickness
of the outermost layer of the cover is smaller than 0.25 mm,
durability of the golf ball decreases. When the thickness of the
outermost layer of the cover is larger than 2.5 mm, a repulsive
force of the golf ball decreases, and thus a carry thereof
decreases. The cover of the golf ball according to the present
invention can be formed with a plurality of layers. In this
situation, a total thickness of the cover (cl) is 0.4-5.0 mm,
preferably 0.5-3.0 mm. A ratio of the coating thickness (PL) to the
cover thickness (cl) (PL/cl) is preferably 0.05-0.4. When the cover
is formed with a single layer, the thickness of the outermost layer
of the cover equals the whole thickness of the cover.
[0033] It is preferable that, a flexural modulus of the outermost
layer of the cover is 2000-50000 N/cm.sup.2. By setting the value
within this range, adherence of the coating thereto can further be
improved, and the peeling of the coating can decrease.
[0034] <Cover>
[0035] In the present invention, a material of the cover is not
specifically limited. An ionomer resin can be used, such as a
binary copolymer of .alpha.-olefin and .alpha.,.beta.-unsaturated
carboxylic acid having a carbon number of 3-8, that is produced by
neutralizing at least a part of the carboxyl group with metal ion.
Also listed as the ionomer resin is a ternary copolymer of
.alpha.-olefin, .alpha.,.beta.-unsaturated carboxylic acid having a
carbon number of 3-8 and .alpha.,.beta.-unsaturated carboxylate
having a carbon number of 2-22, that is produced by neutralizing at
least a part of the carboxyl group with metal ion.
[0036] As the above-mentioned .alpha.-olefin, ethylene, propylene,
1-butene, 1-pentene, for example, are employed, wherein ethylene is
particularly preferable. As the above-mentioned .alpha.,
.beta.-unsaturated carboxylic acid having a carbon number of 3-8,
acrylic acid, methacrylic acid, fumaric acid, maleic acid, crotonic
acid, for example, are employed, wherein acrylic acid and
methacrylic acid are particularly preferable. As the
above-mentioned .alpha., .beta.-unsaturated carboxylate, methyl
ester, ethyl ester, propyl ester, n-butyl ester, isobutyl ester or
the like of acrylic acid, methacrylic acid, fumaric acid, maleic
acid and the like, for example, are employed, wherein acrylic ester
and methacrylic ester are particularly preferable.
[0037] Examples of the metal ion for neutralizing at least a part
of the carboxyl group in the copolymer of .alpha.-olefin and
.alpha.,.beta.-unsaturated carboxylic acid or the ternary copolymer
of .alpha.-olefin, .alpha.,.beta.-unsaturated carboxylic acid and
.alpha.,.beta.-unsaturated carboxylate as described above include
sodium ion, lithium ion, zinc ion, magnesium ion, potassium ion,
and the like.
[0038] The specific examples of the ionomer resin as described
above are those which are commercially available from Du
Pont-Mitsui Polychemicals Co., Ltd. under the trade names of
Hi-Milan 1555 (Na), Hi-Milan 1557 (Zn), Hi-Milan 1605 (Na),
Hi-Milan 1706 (Zn), Hi-Milan 1707 (Na), Hi-Milan AM7318 (Na),
Hi-Milan AM7315 (Zn), Hi-Milan AM7317 (Zn), Hi-Milan AM7311 (Mg),
Hi-Milan MK7320 (K), Hi-Milan 1856 (Na), Hi-Milan 1855 (Zn),
Hi-Milan AM7316 (Zn), and the like.
[0039] The ionomer resins commercially available from Du Pont
further include Surlyn 8945 (Na), Surlyn 8940 (Na), Surlyn 9910
(Zn), Surlyn 9945 (Zn), Surlyn 7930 (Li), Surlyn 7940 (Li), Surlyn
AD8265 (Na), Surlyn AD8269 (Na), and the like.
[0040] Ionomer resins commercially available from ExxonMobil
Chemical Company include lotek 7010 (Zn), lotek 8000 (Na) and the
like. It is noted that, Na, Zn, K, Li, and Mg shown in the brackets
after the trade names of the ionomer resins described above
indicate the neutralizing metal ion species thereof. In the present
invention, the ionomer resin used as the base resin of the cover
may be a mixture of two or more kinds of those illustrated above,
or a mixture of two or more kinds of the ionomer resins neutralized
with a bivalent metal ion and the ionomer resin neutralized with a
monovalent metal ion as illustrated above.
[0041] For the cover according to the present invention, one or
more kinds of thermoplastic elastomer having a rubber component can
be mixed with the ionomer resin for use. The thermoplastic
elastomer having a rubber component is a block copolymer having a
conjugated diene component such as a butadiene block or an isoprene
block. As the conjugated diene compound, for example, one or two or
more kinds can be selected from butadiene, isoprene,
1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Among these,
butadiene, isoprene and the combination thereof are particularly
preferable.
[0042] Specific examples of the thermoplastic elastomer include a
styrene-butadiene-styrene block copolymer (SBS structure), a
styrene-ethylene-butylene-styrene block copolymer formed by
hydrogenating the double bonded portion of butadiene thereof (SEBS
structure), a styrene-isoprene-styrene block copolymer (SIS
structure), a styrene-ethylene-propylene-styrene block copolymer
formed by hydrogenating the double bonded portion of isoprene
thereof (SEPS structure), and modified products thereof. An example
of the block copolymer having the SEBS or SEPS structure with a
hydroxyl group added to the end portion thereof is commercially
available from Kuraray Co. under the trade name of HG-252.
[0043] A part of the copolymer of the SBS, SEBS, SIS, or SEPS
structure described above may be modified with an epoxy group. The
styrene-butadiene-styrene block copolymer (SBS structure) having a
polybutadiene block containing an epoxy group, for example, may be
a block copolymer having polystyrene at both terminal ends and
having polybutadiene containing an epoxy group as an intermediate
portion of the chain, wherein a portion or all of the double bonds
of the polybutadiene portion is hydrogenated.
[0044] The styrene-isoprene-styrene block copolymer (SIS structure)
having a polyisoprene block containing an epoxy group may be a
block copolymer having polystyrene at both terminal ends and having
polyisoprene containing an epoxy group as an intermediate portion
of the chain, wherein a portion or all of the double bonds of the
polyisoprene portion is hydrogenated. A specific example of a diene
block copolymer modified with an epoxy group includes Epofriend
from Daicel Chemical Industries, Ltd.
[0045] Other thermoplastic elastomers include a polyamide
thermoplastic elastomer commercially available from Toray
Industries, Ltd. under the trade name of Pebax, a polyester
thermoplastic elastomer commercially available from Du Pont-Toray
Co., Ltd. under the trade name of Hytrel, a polyurethane
thermoplastic elastomer commercially available from BASF
Polyurethane Elastomers, Ltd. under the trade name of Elastollan,
and the like.
[0046] In the present invention, the cover composition may properly
be blended with additives such as a pigment, an antioxidant, a
plasticizer, a dispersant, and an ultraviolet absorber as
necessary.
[0047] <Cover Formation>
[0048] To form the cover as described above on a surface of a core,
first the cover composition is prepared by mixing the base resin of
the cover with additives such as a pigment, a dispersant, an
antioxidant, an ultraviolet absorber, and a photo-stabilizer as
needed, and then heating the mixture with mixing for 0.5-15 minutes
at 150-250.degree. C. using an internal mixer such as a twin-shaft
kneading-type extruder, a Banbury mixer or a kneader. The cover
composition may directly cover the core, or it may cover the core
with another layer such as an intermediate layer interposed
therebetween.
[0049] The cover may cover the core with a conventionally known
method which is not specifically limited. As an example, the cover
composition may be formed into a half-shell shape, and a pair of
the half-shells may cover the core to form a sphere with heating at
130-170.degree. C. for 1-15 minutes. Alternatively, the cover may
be formed by injection-molding the cover composition onto the core.
During the formation, the cover is formed with dimples on a surface
of the ball.
[0050] In the present invention, the coating as described above is
formed on the outer surface of the cover. A conventionally known
application method can be adopted to form the coating on the cover.
A spray gun or an electrostatic painting, for example, can be
employed. When two-component mixture-type paint including the
above-described polyol and isocyanate is to be applied, the two
components are previously mixed or mixed just before the
application. When the paint is dried after the application, it is
generally preferred that the drying temperature is lower than
50.degree. C. A drying period, which is generally 0.5-5 hours, may
suitably be determined depending on the kind of the coating resin
or the like.
[0051] The golf ball according to the present invention is applied
to a golf ball having any structure which is formed with a core, a
cover covering a surface of the core and a coating applied on a
surface of the cover. A thread layer or an intermediate layer, for
example, can also be formed between the core and the cover.
[0052] <Core>
[0053] In the present invention, the core is formed with a
vulcanizate of a rubber composition formed by blending base rubber
with organic peroxide as a cross-linker and
.alpha.,.beta.-unsaturated carboxylic acid or metal salt thereof as
a co-crosslinker. Hardness of the core is adjusted by changing the
type of the base rubber or a degree of cross-linking.
[0054] The base rubber used in the rubber composition for the core
may be diene rubber conventionally used in the core of the solid
golf ball, for example natural rubber or synthetic rubber. Examples
of the synthetic rubber include an ethylene-propylene-diene ternary
copolymer (EPDM), butadiene rubber (BR), isoprene rubber (IR),
styrene-butadiene rubber (SBR), and acrylonitrile-butadiene rubber
(NBR), and one or two or more kinds thereof may be mixed for use.
Among these, so-called high cis 1,4-polybutadiene rubber containing
at least 40%, preferably at least 80% of cis structure is suitably
used.
[0055] The aforementioned organic peroxide is added as a
cross-linker or a curing agent. Specific examples of the organic
peroxide include dicumyl peroxide, 1,1-bis(t-butyl
peroxy)-3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butyl
peroxy)hexane, and di-t-butyl peroxide, and dicumyl peroxide is
preferably used. A blended amount of the organic peroxide is
preferably 0.3-2.0 parts by mass, particularly 0.3-1.0 parts by
mass with respect to 100 parts by mass of the base rubber.
[0056] As .alpha.,.beta.-unsaturated carboxylic acid blended as the
co-crosslinker, .alpha.,.beta.-unsaturated carboxylic acid having a
carbon number of 3-8 such as acrylic acid or methacrylic acid can
be used. Further, as metal salt of .alpha.,.beta.-unsaturated
carboxylic acid, zinc salt, magnesium salt, sodium salt, or the
like thereof can be listed. Among these, zinc diacrylate which adds
high resilience is preferable. The blended amount of the metal salt
of .alpha.,.beta.-unsaturated carboxylic acid is preferably 15-45
parts by mass, more preferably 25-40 parts by mass with respect to
100 parts by mass of the base rubber.
[0057] In addition to the above-described components, the rubber
composition for the core can properly be blended with common
additives included in the core of the golf ball, such as a specific
gravity adjustment agent, an antioxidant, a plasticizer, a
dispersant, an ultraviolet absorber, and a pigment as needed. As
the specific gravity adjustment agent, inorganic salt such as zinc
oxide, barium sulfate or calcium carbonate, metal powder having
high specific gravity such as tungsten or molybdenum powder, and a
mixture thereof can be used. Phenol compound can be used as the
antioxidant.
EXAMPLES
Examples 1-6 and Comparative Examples 1-4
[0058] (Fabrication of Core)
[0059] A core having an outside diameter of 39.0 mm was fabricated
by filling a mold with a rubber composition containing 100 parts by
mass of high cis butadiene rubber (BR18, produced by JSR
Corporation.), 36 parts by mass of zinc diacrylate, 17.2 parts by
mass of zinc oxide, 0.4 parts by mass of dicumyl peroxide, and 0.9
parts by mass of bis(pentachlorophenyl)disulfide, and vulcanizing
in a mold under compression for 20 minutes at 160.degree. C.
[0060] (Covering of Cover)
[0061] A cover composition was then prepared by mixing 25 parts by
mass of Surlyn 8945 (sodium-neutralized ethylene-methacrylate
copolymer ionomer) produced by Du Pont, 25 parts by mass of Surlyn
9945 (zinc-neutralized ethylene-methacrylate copolymer ionomer)
produced by Du Pont, 35 parts by mass of HG252 produced by Kuraray
Co., 15 parts by mass of Epofriend A1010 produced by Daicel
Chemical Industries, Ltd., 2 parts by mass of titanium oxide, and 2
parts by mass of barium sulfate, and a surface of the
aforementioned core was covered with the composition by an
injection molding machine to form a two-piece golf ball body having
a diameter of 42.8 mm.
[0062] (Formation of Coating)
[0063] PTMG650 produced by BASF as bifunctional polyol and
trimethylol propane produced by Koei Chemical Co., Ltd. as
trifunctional polyol were blended in ratios shown in Tables 1 and
2, diluted with toluene solvent so that polyol constitutes 30% by
mass in a solid state, and added with 0.02% by weight of dibutyl
tin dilaurate as a catalyst to prepare a main agent. A curing
agent, on the other hand, was prepared by diluting N3500,
hexamethylene diisocyanate produced by Sumika Bayer Urethane Co.,
Ltd., with toluene so as to constitute 60% in a solid state.
[0064] Each paint was prepared by blending the above-described main
component and curing agent in an equivalent ratio of 1:1.2 and
mixing for 5 minutes. The golf ball body formed as above was
rotated at 150 rpm, and the paint prepared as above was sprayed on
the ball body with moving an air gun upward and downward to form a
coating on the surface of the ball body. A golf ball was obtained
by a curing step for 120 minutes at 50.degree. C. thereafter.
Specifications of golf balls in examples 1-6 and comparative
examples 1-4 are shown in Tables 1 and 2.
1 TABLE 1 Examples 1 2 3 4 5 6 7 8 Composition BR18 100 100 100 of
core zinc diacrylate 36 36 36 zinc oxide 17.2 16.7 16.2
bis(pentachlorophenyl)dis- ulfide 0.9 0.9 0.9 dicumyl peroxide 0.4
0.4 0.4 Composition Surlyn 8945 25 of cover Surlyn 9945 25 HG252 35
Epofriend A1010 15 Composition trimethylol propane 1.5 1.5 1.5 1.5
1.2 2.3 1.5 1.5 of coating /polytetramethylene glycol Thickness of
outermost layer of cover(mm):CL 1.9 1.9 1.9 1.9 1.9 1.9 1.4 0.8
Thickness of coating(.mu.):PL 30 50 80 120 50 50 50 50
R(PL/CL/1000) 0.016 0.026 0.042 0.063 0.026 0.026 0.036 0.063
50%-modulus(MPa) 22.3 22.3 22.3 22.3 16.2 28.8 22.3 22.3 DRY spin
rate(rpm) 6700 6600 6500 6400 6700 6500 6500 6300 WET spin
rate(rpm) 2950 3050 3000 2950 3050 3000 3050 3000 Spin retention(%)
44 46 46 46 46 46 47 47
[0065]
2 TABLE 2 Comparative examples 1 2 3 4 5 Composition BR18 100 100
of core zinc diacrylate 36 36 zinc oxide 17.2 18.2
bis(pentachlorophenyl)disulfid- e 0.9 0.9 dicumyl peroxide 0.4 0.4
Composition Surlyn 8945 25 of cover Surlyn 9945 25 HG252 35
Epofriend A1010 15 Composition trimethylol propane 1.5 1.5 1.5 0.5
1.5 of coatin /polytetramethylene glycol Thickness of outermost
Layer of cover(mm):CL 1.9 1.9 1.9 1.9 3.2 Thickness of
coating(.mu.):PL 8 18 140 50 30 R(PL/CL/1000) 0.004 0.009 0.074
0.026 0.009 50%-modulus(MPa) 22.3 22.3 22.3 4.2 22.3 DRY spin
rate(rpm) 6350 6400 7000 6800 6950 WET spin rate(rpm) 2400 2450
2750 2400 2500 Spin retention(%) 38 38 39 35 36
Examples 7, 8 and Comparative Example 5
[0066] A golf ball was fabricated as in the example 1, except for
different composition of the core as shown in Tables 1 and 2.
[0067] (Evaluation Method)
[0068] Specimens and golf balls obtained with the above-described
method based on specifications of the examples and comparative
examples were evaluated by the following method.
[0069] (1) 50%-Modulus of Coating (MPa)
[0070] Paint prepared as above was applied on a coating glass plate
and was cured. The coating formed on the glass plate was peeled to
prepare a size-4 dumbbell specimen having a thickness of 0.2 mm
with the coating, and a tensile test defined by JIS K6251 was
performed. A tensile strength to obtain 50% elongation of the
coating was measured as a 50%-modulus.
[0071] (2) Spin Retention
[0072] A sand wedge club was attached to a swing robot manufactured
by True-Temper to hit a ball at a head speed of 21 m/s. The ball
was accordingly shot and a mark applied to the ball were taken
through sequential photography so as to measure a spin rate. The
measurement was done under a normal dry condition and a wet
condition generated by wetting the ball and club face with water. A
spin retention is defined as a value of, spin rate under wet
condition/spin rate under dry condition.times.100. A higher value
indicates a better spin retention.
[0073] (Evaluation Result)
[0074] It is obvious from Table 1 that all the golf balls in the
examples 1-8 according to the present invention show good spin
retention. On the contrary, the comparative examples 1, 2, which
have small coating thicknesses (PL) such as 8 .mu.m and 18 .mu.m
and value R smaller than 0.01, and the comparative example 3, which
has large coating thickness (PL) such as 140 .mu.m, show low spin
retention. The comparative example 4, which has the coating
thickness (PL) of 50 .mu.m but the 50%-modulus of the coating as
low as 4.2 MPa, also shows low spin retention. In addition, the
comparative example 5, which has the coating thickness (PL) of 30
.mu.m but the thickness of the outermost layer of the cover (CL) as
large as 3.2 mm and value R smaller than 0.01, also shows low spin
retention.
[0075] The embodiment disclosed herein should be considered
illustrative in all points, rather than limiting. The scope of the
present invention is not indicated by the descriptions above, but
by the appended claims. All modifications that fall in the
equivalent spirit and scope of the claims are intended to be
included in the present invention.
[0076] As described above, by setting the coating thickness and the
50%-modulus of the coating within prescribed ranges and setting the
ratio of the thickness of the outermost layer of the cover and the
coating thickness to a prescribed value, the golf ball according to
the present invention can retain the high spin retention, and the
coating follows deformation of the cover without peeling off the
cover even for the large deformation caused by hitting the golf
ball with a driver or the like.
[0077] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
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