U.S. patent application number 09/788618 was filed with the patent office on 2001-07-26 for golf ball cover stocks and golf balls.
Invention is credited to Ichikawa, Yasushi, Kashiwagi, Shunichi, Takesue, Rinya.
Application Number | 20010009947 09/788618 |
Document ID | / |
Family ID | 26566659 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009947 |
Kind Code |
A1 |
Takesue, Rinya ; et
al. |
July 26, 2001 |
Golf ball cover stocks and golf balls
Abstract
A cover stock composed mainly of a heated mixture of a
thermoplastic polyurethane elastomer and a polyolefin oligomer or
polyolefin which has been modified with functional groups is
suitable for the manufacture of golf balls. The cover made of the
stock has improved scuff resistance.
Inventors: |
Takesue, Rinya;
(Chichibu-shi, JP) ; Ichikawa, Yasushi;
(Chichibu-shi, JP) ; Kashiwagi, Shunichi;
(Chichibu-shi, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
WASHINGTON
DC
20037-3213
US
|
Family ID: |
26566659 |
Appl. No.: |
09/788618 |
Filed: |
February 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09788618 |
Feb 21, 2001 |
|
|
|
09179839 |
Oct 28, 1998 |
|
|
|
Current U.S.
Class: |
525/123 ;
525/126; 525/454; 525/455 |
Current CPC
Class: |
C08L 75/04 20130101;
C08L 75/04 20130101; C08L 23/00 20130101; Y10S 525/919
20130101 |
Class at
Publication: |
525/123 ;
525/455; 525/126; 525/454 |
International
Class: |
C08L 075/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 28, 1997 |
JP |
9-311278 |
Oct 28, 1997 |
JP |
9-311279 |
Claims
Although some preferred embodiments have been described, many
modifications and variations may be made thereto in the light of
the above teachings. It is therefore to be understood that within
the scope of the appended claims, the invention may be practiced
otherwise than as specifically described.
1. A golf ball cover stock comprising as a main component a heated
mixture consisting essentially of a thermoplastic polyurethane
elastomer and a polyolefin oligomer or polyolefin which has been
modified with functional groups.
2. The cover stock of claim 1 wherein said heated mixture has a
Shore D hardness of 35 to 55.
3. The cover stock of claim 1 wherein said heated mixture consists
essentially of 90 to 99.9 parts by weight of the thermoplastic
polyurethane elastomer and 10 to 0.1 part by weight of the modified
polyolefin oligomer.
4. The cover stock of claim 1 wherein said polyolefin oligomer
modified with functional groups is an acid-modified polyolefin
oligomer.
5. The cover stock of claim 4 wherein said functional groups are
acid anhydride or carboxyl groups and the modified polyolefin
oligomer has an acid value of 1 to 60 mg KOH per gram.
6. The cover stock of claim 1 wherein said heated mixture consists
essentially of 80 to 99.5 parts by weight of the thermoplastic
polyurethane elastomer and 20 to 0.5 part by weight of the modified
polyolefin.
7. The cover stock of claim 1 wherein said polyolefin modified with
functional groups is an epoxy-modified polyolefin.
8. The cover stock of claim 7 wherein an epoxy component for
introducing epoxy groups is glycidyl methacrylate or glycidyl
acrylate.
9. The cover stock of claim 7, wherein said heated mixture further
contains a component for softening the epoxy-modified polyolefin in
the heated mixture, the softening component being selected from the
group consisting of acrylates, methacrylates and vinyl acetate.
10. A golf ball comprising a cover formed from the cover stock of
claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to cover stocks for golf balls having
improved scuff resistance and golf balls having covers formed of
the stocks.
[0003] 2. Prior Art
[0004] In prior art golf balls, balata or trans-polyisoprene and
ionomer resins are often used as the cover stock. Professional and
skilled golfers prefer golf balls using balata as the cover stock,
because the balata cover balls are good in feel upon full shots
with a driver and the ease of control (or spin susceptibility) upon
approach shots.
[0005] The balata cover balls, however, have the drawback that the
ball surface is marred or fluffed as a consequence of iron shots
because the cover surface can be scraped by grooves across the iron
club face. In addition, balata cover stocks are expensive and low
in productivity because of difficulty to mold and a need for
vulcanization.
[0006] Efforts have been made to seek for cover stocks having good
feel and controllability comparable to the balata while eliminating
the drawbacks of the balata. For example, cover stocks using
thermoplastic polyurethane elastomers as disclosed in U.S. Pat.
Nos. 3,395,109, 4,248,432, and 4,442,282 are relatively inexpensive
as compared with the balata and easy to mold. Golf balls using
these cover stocks offer good feel and controllability comparable
to the balata cover balls. However, covers of thermoplastic
polyurethane elastomers are still unsatisfactory in scuff
resistance upon iron shots. Particularly at low temperatures or in
winter, there is a likelihood that the ball surface can be cracked
and dimples be scraped off by the iron club face.
[0007] Besides, in golf ball cover stocks, metals salts of fatty
acids such as magnesium stearate are generally blended as a
dispersant. In a conventional process involving injection molding a
cover stock having a fatty acid metal salt blended therein around a
core to form a cover and painting the surface of the cover, the
left-over of the fatty acid metal salt on the cover surface can
adversely affect the adhesion of a paint coating to the cover.
SUMMARY OF THE INVENTION
[0008] An object of the invention is to provide a novel and
improved golf ball cover stock capable of producing a golf ball of
improved performance that offers improved scuff resistance against
iron shots, the ease of control upon approach shots, and a very
soft feel without shocks upon driver shots. Another object of the
invention is to provide a golf ball using the cover stock.
[0009] In search of a golf ball cover stock which can offer a
pleasant feel and is improved in controllability and scuff
resistance, we have found that a golf ball cover stock comprising
as a main component a heated mixture of a thermoplastic
polyurethane elastomer and a polyolefin oligomer or polyolefin
which has been modified with functional groups is best suited for
achieving the above and other objects.
[0010] More particularly, according to the invention, a heated
mixture of (1) a thermoplastic polyurethane elastomer, especially a
thermoplastic polyurethane elastomer having a Shore D hardness of
35 to 55 and comprising an aliphatic diisocyanate as the
diisocyanate component and (2) a functional group-modified
polyolefin oligomer or polyolefin which is expected to serve as a
binder on account of the intermolecular interaction with polar
groups (such as hydroxyl groups or urethane bonds) in the
thermoplastic polyurethane elastomer, is used as the main component
of the golf ball cover stock. Golf balls obtained by enclosing
cores with this cover stock substantially solve the problem that as
a consequence of iron shots, the cover surface can be scraped by
grooves across the iron club face and the ball surface is marred or
fluffed. Upon full shots with a driver, the balls offer a very soft
feel without a shock and without a shortage of flight distance.
Therefore, the cover stock of the above-described composition is
significantly improved in function and effect over conventional
cover stocks of thermoplastic polyurethane elastomers.
Additionally, when a functional group-modified polyolefin oligomer
with a relatively low molecular weight is used as component (2) of
the heated mixture, the oligomer also serves as a dispersant for
pigments and thus helps reduce the amount of a fatty acid metal
salt (typically magnesium stearate) blended as the dispersant. The
problem of poor adhesion of a paint coating caused by the presence
of the fatty acid metal salt is thus substantially eliminated.
[0011] Accordingly, the present invention provides a golf ball
cover stock comprising as a main component a heated mixture
consisting essentially of a thermoplastic polyurethane elastomer
and a polyolefin oligomer or polyolefin which has been modified
with functional groups. Also contemplated herein is a golf ball
comprising a core and a cover formed from the inventive cover
stock.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The cover stock for golf balls according to the invention
uses as a main component a heated mixture of (1) a thermoplastic
polyurethane elastomer and (2) a polyolefin oligomer or polyolefin
which has been modified with functional groups.
[0013] The thermoplastic polyurethane elastomer (1) used herein has
a molecular structure consisting of a polyol compound constituting
a soft segment, a monomolecular chain extender constituting a hard
segment, and a diisocyanate.
[0014] The polyol compound is not critical and may be any of
polyester polyols, polyether polyols, copolyester polyols, and
polycarbonate polyols. Exemplary polyester polyols include
polycaprolactone glycol, poly(ethylene-1,4-adipate) glycol, and
poly(butylene-1,4-adipate) glycol; an exemplary polyether polyol is
polyoxytetramethylene glycol; an exemplary copolyester polyol is
poly(diethylene glycol adipate) glycol; and an exemplary
polycarbonate polyol is (hexanediol-1,6-carbonate) glycol. Their
number average molecular weight is about 600 to 5,000, preferably
about 1,000 to 3,000.
[0015] As the diisocyanate, aromatic diisocyanates such as tolylene
diisocyanate (TDI), diphenylmethane diisocyanate (MDI), tolidine
diisocyanate (TODI), and naphthalene diisocyanate (NDI) are
included although aliphatic diisocyanates are preferably used in
consideration of the yellowing resistance of the cover. Examples of
the aliphatic diisocyanate include hexamethylene diisocyanate
(HDI), 2,2,4- or 2,4,4-trimethylhexamethylene diisocyanate (TMDI),
and lysine diisocyanate (LDI). HDI is especially preferred for its
compatibility with another resin upon blending.
[0016] The monomolecular chain extender is not critical and may be
selected from conventional polyhydric alcohols and amines. Examples
include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-propylene
glycol, 1,6-hexylene glycol, 1,3-butylene glycol,
dicyclohexylmethylmethanediamin- e (hydrogenated MDA), and
isophoronediamine (IPDA).
[0017] Of the thermoplastic polyurethane elastomers, those having a
Shore D hardness of 35 to 55, especially 40 to 55 are preferred.
With a Shore D hardness of less than 35, the ball would receive an
increased spin rate and thus travel short when hit with a driver.
With a Shore D hardness of more than 55, the cover would be
insufficiently soft and adversely affect the feel and control when
hit. The specific gravity of the thermoplastic polyurethane
elastomer is not critical and may be adjusted as appropriate
insofar as the objects of the invention are achievable. Preferably
the specific gravity is from 0.9 to 1.5, more preferably from 0.9
to 1.3, especially 1.0 to 1.2.
[0018] As the thermoplastic polyurethane elastomer, there may be
used commercially available ones whose diisocyanate component is
aliphatic, for example, Pandex T7298, EX7895, and T7890 (by
Dai-Nippon Ink & Chemicals K. K.).
[0019] The second essential component of the cover stock according
to the invention is (2-a) a polyolefin oligomer which has been
modified with functional groups or (2-a) a polyolefin which has
been modified with functional groups.
[0020] The modified polyolefin oligomers (2-a) usually have a
number average molecular weight Mn of about 1,000 to 20,000,
preferably about 1,500 to 17,000, more preferably about 1,500 to
16,000, especially about 1,500 to 15,000. Oligomers with Mn of less
than 1,000 are less reactive with the thermoplastic polyurethane
elastomer and sometimes fail to achieve an improvement in scuff
resistance whereas oligomers with Mn of more than 20,000 would not
serve as a dispersant for pigments.
[0021] Exemplary of the modified polyolefin oligomers are
acid-modified polyolefin oligomers, epoxy group-modified polyolefin
oligomers, hydroxyl group-modified polyolefin oligomers, and amino
group-modified polyolefin oligomers. Examples of the olefin
component include ethylene, propylene, butene, hexene and octene,
with the ethylene and propylene being preferred.
[0022] In the practice of the invention, acid-modified polyolefin
oligomers are especially preferred as the modified polyolefin
oligomer. Examples of the acid component include maleic acid,
maleic anhydride, and sulfonic acid. Preferred are acid components
having carboxyl groups or acid anhydride groups, such as maleic
acid and maleic anhydride. Together with the acid-modified
polyolefin oligomers, polymerizable monomers having an aliphatic
unsaturated bond other than the olefin, for example, acrylates,
methacrylates and vinyl acetate may be used as a comonomer for the
purpose of softening the polyolefin oligomer. Exemplary acrylates
and methacrylates are esters of (meth)acrylic acid with aliphatic
alcohols of 1 to 4 carbon atoms in which some of the hydrogen atoms
attached to carbon atoms may be replaced by hydroxyl groups or the
like, for example, methyl (meth)acrylate, ethyl (meth)acrylate and
butyl (meth)acrylate.
[0023] The acid-modified polyolefin oligomers preferably have an
acid value of 1 to 60 mg KOH per gram, more preferably 10 to 60 mg
KOH per gram as measured by titration assay. A polyolefin oligomer
with an acid value of less than 1 mg KOH/g would react a very
little with the thermoplastic polyurethane elastomer and be less
dispersible. A polyolefin oligomer with an acid value of more than
60 mg KOH/g would react too much with the thermoplastic
polyurethane elastomer so that the mixture might become less
flowing and difficult to mold.
[0024] Suitable acid-modified polyolefin oligomers are commercially
available, for example, under the trade name of Umex 200 and 1010
from Sanyo Chemicals K. K. and Bondyne AX8390 from Sumitomo
Chemical K. K.
[0025] The functional group-modified polyolefins (2-b) usually have
a number average molecular weight Mn of about 10,000 to 50,000,
preferably about 15,000 to 48,000, more preferably about 17,000 to
45,000.
[0026] Exemplary of the modified polyolefins are acid-modified
polyolefins, epoxy group-modified polyolefins, hydroxyl
group-modified polyolefins, and amino group-modified polyolefins.
Examples of the olefin component include ethylene, propylene,
butene, hexene and octene, with the ethylene and propylene being
preferred.
[0027] In the practice of the invention, epoxy-modified polyolefins
are especially preferred as the modified polyolefin. Examples of
the epoxy component include glycidyl methacrylate and glycidyl
acrylate.
[0028] In addition to the olefin and epoxy components,
polymerizable monomers having an aliphatic unsaturated bond other
than the olefin, for example, acrylates, methacrylates and vinyl
acetate may be used as a comonomer for the purpose of softening the
polyolefin. Exemplary acrylates and methacrylates are esters of
(meth)acrylic acid with aliphatic alcohols of 1 to 4 carbon atoms
in which some of the hydrogen atoms attached to carbon atoms may be
replaced by hydroxyl groups or the like, for example, methyl
(meth)acrylate, ethyl (meth)acrylate and butyl (meth)acrylate.
[0029] Examples of the epoxy-modified polyolefin include
ethylene/glycidyl (meth)acrylate, ethylene/n-butyl
acrylate/glycidyl (meth)acrylate, ethylene/methyl acrylate/glycidyl
(meth)acrylate, ethylene/acrylate/glyci- dyl (meth)acrylate, and
ethylene/glycidyl (meth)acrylate/vinyl acetate copolymers. Suitable
epoxy-modified polyolefins are commercially available, for example,
under the trade name of Elvaloy AS and EP4934-6 from Mitsui-duPont
Polychemical K. K.
[0030] The golf ball cover stock of the invention is obtained by
mixing a thermoplastic polyurethane elastomer with a functional
group-modified polyolefin oligomer or polyolefin and heating the
mixture until the desired properties are achieved. When the
polyolefin oligomer is used, the preferred mixing proportion is 90
to 99.9 parts, especially 95 to 99.5 parts by weight of the
thermoplastic polyurethane elastomer and 10 to 0.1 part, especially
5 to 0.5 parts by weight of the modified polyolefin oligomer, per
100 parts by weight of the mixture. A polyolefin oligomer content
in excess of 10 parts by weight would lead to poor flight
performance. With a polyolefin oligomer content of less than 0.1
part by weight, the cover would be low in scuff resistance, failing
to produce a satisfactory golf ball. When the polyolefin is used,
the preferred mixing proportion is 80 to 99.5 parts, especially 90
to 99.5 parts by weight of the thermoplastic polyurethane elastomer
and 20 to 0.5 part, especially 10 to 0.5 parts by weight of the
modified polyolefin, per 100 parts by weight of the mixture. A
polyolefin content in excess of 20 parts by weight would lead to
poor flight performance. With a polyolefin content of less than 0.5
part by weight, the cover would be low in scuff resistance, failing
to produce a satisfactory golf ball.
[0031] The method of mixing and heating these components is not
critical. In general, using internal mixers such as kneading
twin-screw extruders, Banbury mixers and kneaders, the components
are mixed and heated at a temperature of about 150 to 250.degree.
C. for about 1/2 to 15 minutes.
[0032] The heated mixture should preferably have a Shore D hardness
of 35 to 55, and more preferably 45 to 55. With a Shore D hardness
of less than 35, the resulting cover would become so soft that the
ball might receive an increased spin rate and thus travel short
when hit with a driver. With a Shore D hardness of more than 55,
the resulting golf ball would fail to receive an appropriate back
spin rate upon approach shots and become difficult to control. The
heated mixture should preferably have a specific gravity of 0.9 to
1.5, more preferably 0.9 to 1.3, and most preferably 1.0 to 1.2,
though the invention is not limited thereto.
[0033] In the present invention, the heated mixture of a
thermoplastic polyurethane elastomer and a modified polyolefin
oligomer or polyolefin constitutes the main component of the golf
ball cover stock. The main component encompasses both the resin
component of the cover stock consisting solely of the heated
mixture and the resin component of the cover stock containing
another resin or resins in addition to the heated mixture. Where
the resin component of the cover stock consists solely of the
heated mixture, non-resinous components such as titanium dioxide
and barium sulfate are added in minor amounts. Then the hardness of
the cover stock is substantially equal to that achieved when the
thermoplastic polyurethane elastomer is used alone as the resin
component. Where the resin component of the cover stock contains
another resin or resins in addition to the heated mixture, ionomer
resins, thermoplastic polystyrene elastomers and thermoplastic
polyester elastomers may be used as the other resin. Preferably,
the heated mixture of the two resin components according to the
invention accounts for at least 70% by weight, more preferably at
least 80% by weight of the cover stock resin component.
[0034] In addition to the essential components, various additives
are added to the cover stock according to the invention, if
necessary. Such additives are, for example, pigments, dispersants,
antioxidants, UV absorbers and photostabilizers.
[0035] The cover stock of the invention is prepared, for example,
by charging an internal mixer such as a kneading twin-screw
extruder, Banbury mixer or kneader with the components, and mixing
and heating them at a temperature of about 150 to 250.degree. C.
for about 1/2 to 15 minutes. In the mixing and heating step, the
two resin components and other additives may be mixed and heated
together to form a cover stock composition. Alternatively, the two
resin components are mixed and heated before the mixture is further
mixed with other additives.
[0036] The golf ball of the invention is comprised of a core and a
cover formed thereon from the inventive cover stock. Included are
wound golf balls and solid golf balls such as two, three and
multi-piece solid golf balls.
[0037] In the manufacture of the golf ball of the invention,
components other than the cover may be prepared by conventional
well-known methods. Wound cores or solid cores are prepared in a
conventional manner before they are enclosed with the inventive
cover stock.
[0038] For example, the solid center for wound golf balls or the
solid core for solid golf balls is prepared by blending 100 parts
by weight of cis-1,4-polybutadiene with 10 to 60 parts by weight of
a vulcanizing or crosslinking agent composed of an
.alpha.,.beta.-monoethylenically unsaturated carboxylic acid such
as acrylic acid or methacrylic acid or a metal salt thereof, a
functional monomer such as trimethylolpropane methacrylate, or a
mixture thereof, 5 to 30 parts by weight a filler such as zinc
oxide or barium sulfate, 0.5 to 5 parts by weight of a peroxide
such as dicumyl peroxide, and optionally 0.1 to 1 part by weight of
an antioxidant to form a rubber composition, and press molding and
vulcanizing (or crosslinking) the rubber composition, for example,
by heating under pressure at 140 to 170.degree. C. for 10 to 40
minutes, thereby forming a spherical vulcanized part. The liquid
center for wound golf balls are prepared, for example, by forming a
hollow spherical center bag from the above-described rubber
composition and filling the bag with a liquid in a well-known
manner.
[0039] The core for wound golf balls is prepared by winding thread
rubber under tension around the solid or liquid center prepared
just above. The thread rubber used herein may be conventional one,
for example, the one obtained by blending natural rubber or
synthetic rubber (e.g., polyisoprene) with additives such as an
antioxidant, vulcanization accelerator and sulfur and molding and
vulcanizing the resulting rubber composition.
[0040] The weight, diameter, hardness and other parameters of the
solid or liquid center, solid core, and wound core may be adjusted
as appropriate insofar as the objects of the invention are
achievable.
[0041] The method of enclosing a core with the cover stock of the
invention is not critical. Well-known methods are employable. For
example, a golf ball may be prepared by preforming hemispherical
shells from the cover stock, enclosing a core with a pair of
preformed shells, and effecting compression molding at about 120 to
170.degree. C. for about 1 to 5 minutes. Alternatively, the molten
cover stock is directly injection molded over a core in a mold.
[0042] The gage of the cover may be properly adjusted insofar as
the objects of the invention are achievable. Usually the cover has
a gage of 1 to 4 mm, especially 1.3 to 2.1 mm. The cover is not
limited to a single layer and may be formed from two or more
layers. In the case of a multi-layer cover, a layer(s) of the
inventive cover stock may be combined with a layer(s) of
conventional cover stock.
[0043] During or after the molding of the cover, a multiplicity of
dimples are usually formed on the ball surface. If necessary, the
molding of the cover is followed by surface treatments including
stamping and paint coating. Since the cover of the inventive cover
stock is well adherent, an adherent coating can be formed on the
cover surface. The surface treatment can be carried out in a
satisfactory manner.
[0044] The golf balls of the invention for competition use are
prepared in accordance with the Rules of Golf to a diameter of not
less than 42.67 mm and a weight of not greater than 45.93 g.
[0045] There has been described a golf ball cover stock which
offers a very soft feel without a substantial shock, the ease of
control and improved scuff resistance.
EXAMPLE
[0046] Examples of the invention are given below by way of
illustration and not by way of limitation.
[0047] Examples 1-4 and Comparative Examples 1-4
[0048] Solid cores having a diameter of 38.6 mm, a weight of 34.1
grams and a deflection of 3.0 mm under an applied load of 100 kg
were prepared using a core composition containing
cis-1,4-polybutadiene as a main component.
[0049] Next, the solid cores were set in molds, and cover stocks of
the formulation shown in Table 1 obtained by heat kneading at
185.degree. C. for 1/2 minute were injection molded over the cores
to a gage of 2.0 mm, producing two-piece solid golf balls of
Examples 1-4 and Comparative Examples 1-4.
[0050] The two-piece golf balls were examined for hardness, initial
velocity, scuff resistance, contact angle and coating adhesion by
the following tests. The results are shown in Table 2.
[0051] Hardness
[0052] Ball hardness was expressed by a deflection (mm) of a ball
under an applied load of 100 kg.
[0053] Initial Velocity
[0054] An initial velocity (m/s) was measured by an initial speed
meter of the same type as prescribed by USGA.
[0055] Scuff Resistance
[0056] Using a swing robot machine having a pitching wedge mounted,
the ball was hit at a head speed of 33 m/s. The surface state of
the ball after hitting was rated on a 5-point scale by a panel of
ten observers. The rating is an average of ten ratings.
[0057] 5: ball surface intact, or very slight club face dents
[0058] 4: some club face dents, but no fluff on the cover
surface
[0059] 3: some club face dents, fluffy cover surface
[0060] 2: fluffy cover surface, cracks
[0061] 1: dimples scraped off
[0062] Contact Angle and Coating Adhesion
[0063] The respective cover stock resins were melted at 200.degree.
C. and press molded into test sheets of 1 mm thick. Each test sheet
was conditioned at 23.degree. C. and RH 50%. A drop of distilled
water was applied to the test sheet, and a contact angle with water
was measured. A urethane paint for golf balls was applied to the
test sheet to a thickness of 15 .mu.m, dried at 50.degree. C., and
left to stand at room temperature for 48 hours.
[0064] Then, a crosscut adhesive tape test was carried out
according to JIS K-5400. The coated sheet was scribed in
perpendicular directions at a line spacing of 1 mm to define 100
square sections in total. Adhesive tape was applied to the crosscut
sheet and then peeled therefrom. After tape peeling, the coating
was visually observed to inspect whether or not coating sections
were separated, and rated according to the following criteria.
1 Point Remarks 10 Each cut line was narrow and flanked by smooth
edges. No separation was found at intersections between cut lines.
No square sections were peeled. 8 Slight separation was found at
intersections between cut lines. No square sections were peeled.
Defective areas accounted for less than 5% of the total area of
square sections. 6 Separation was found at opposite edges of cut
lines and at intersections between cut lines. Defective areas
accounted for 5% to less than 15% of the total area of square
sections. 4 Separation was found over some extent along cut lines.
Defective areas accounted for 15% to less than 35% of the total
area of square sections. 2 Separation was found over a more extent
along cut lines. Defective areas accounted for 35% to less than 65%
of the total area of square sections. 0 Separation was found over a
further extent along cut lines. Defective areas accounted for 65%
or more of the total area of square sections.
[0065]
2 TABLE 1 Comparative Comparative Example Example Example Example
Cover stock 1 2 3 1 2 4 3 4 Composition Pandex 95 91 95 100 95 100
100 100 (pbw) T7298 Umex 1010 5 9 0.7 Umex 2000 5 Sanwax 5 0.7
131-P Titanium 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 dioxide Magnesium
0.7 0.7 0.7 0.7 0.7 0.7 stearate Specific gravity 1.16 1.14 1.16
1.18 1.16 1.17 1.18 1.17 Hardness (Shore D) 48 48 48 48 48 48 48 48
Pandex T7298: non-yellowing thermoplastic polyurethane elastomer,
Shore D hardness 48, Dai-Nippon Ink & Chemicals K.K. Umex 1010:
polypropylene modified with maleic anhydride, acid value 52 mg
KOH/g, Mn 7000, Sanyo Chemicals K.K. Umex 2000: polyethylene
modified with maleic anhydride, acid value 30 mg KOH/g, Mn 16000,
Sanyo Chemicals K.K. Sanwax 131-P: polyethylene wax, Mn 3500, Sanyo
Chemicals K.K.
[0066]
3 TABLE 2 Comparative Comparative Example Example Example Example 1
2 3 1 2 4 3 4 Ball 45.4 45.1 45.4 45.7 45.3 45.7 45.7 45.7 weight
(g) Ball 2.73 2.70 2.70 2.73 2.65 2.83 2.76 2.76 hardness (mm)
Initial 75.3 75.2 75.3 75.4 75.3 75.4 75.5 75.5 velocity (m/s)
Scuff 4.3 4.8 3.9 3.6 3.1 4.4 3.7 3.7 resistance (point) Contact 60
51 69 75 75 70 75 74 angle (.degree.) Coating 10 10 10 8 8 10 8 9
adhesion (point)
[0067] It is evident from Table 2 that inventive golf balls using
cover stocks based on heated mixtures of a thermoplastic
polyurethane elastomer and a functional group-modified polyolefin
oligomer are improved in adhesion of paint coating to the cover and
scuff resistance.
[0068] Examples 5-9 and Comparative Examples 5-6
[0069] Solid cores having a diameter of 38.6 mm, a weight of 34.1
grams and a deflection of 3.0 mm under an applied load of 100 kg
were prepared using a core composition containing
cis-1,4-polybutadiene as a main component.
[0070] Next, cover stocks in pellet form were prepared by mixing
components of the formulation shown in Table 3 in a kneading
twin-screw extruder at 185.degree. C. for 1/2 minute and extruding
the mixture. The solid cores were set in molds, and the cover
stocks were injection molded over the cores to a gage of 2.1 mm,
producing two-piece solid golf balls of Examples 5-9 and
Comparative Examples 5-6.
[0071] The two-piece golf balls were examined for weight, hardness,
initial velocity, and scuff resistance as in Example 1 and for
hitting feel by the following test. The results are shown in Table
4.
[0072] Hitting Feel
[0073] With a driver (W#1) PRO 230 Titan (loft angle 11.degree.,
shaft Harmotec Lite HM50J(HK), hardness S, balance D2, by
Bridgestone Sports Co., Ltd.), an actual hitting test was performed
by a panel of ten golfers with a head speed of about 45 m/sec
(HS45). The ball was rated according to the following criterion.
For each ball, the rating given by the majority of golfers is
shown.
[0074] Exc.: very soft feel with little shock
[0075] Good: soft feel with little shock
[0076] Av: average
[0077] Poor: poor feel with heavy shocks
4 TABLE 3 Comparative Example Example Cover stock 5 6 7 8 9 5 6
Com- Pandex 95 90 95 90 85 100 95 posi- T7298 tion Elvaloy 5 10
(pbw) EP4934-6 Elvaloy AS 5 10 15 PE LF660H 5 Titanium 2.5 2.5 2.5
2.5 2.5 2.5 2.5 dioxide Magnesium 0.7 0.7 0.7 0.7 0.7 0.7 0.7
stearate Specific gravity 1.16 1.14 1.16 1.14 1.12 1.18 1.16
Hardness (Shore D) 48 48 48 48 48 48 50 Pandex T7298: non-yellowing
thermoplastic polyurethane elastomer, Shore D hardness 48,
Dai-Nippon Ink & Chemicals K.K. Elvaloy EP4934-6: low glycidyl
methacrylate type ethylene-acrylate-glycidyl methacrylate random
terpolymer, E.I. duPont Elvaloy AS: high glycidyl methacrylate type
ethylene-acrylate-glycidyl methacrylate random terpolymer, E.I.
duPont PE LF660H: low density polyethylene resin, Shore D hardness
55, Mitsubishi Chemical K.K.
[0078]
5 TABLE 4 Comparative Example Example 5 6 7 8 9 5 6 Ball 45.5 45.3
45.5 45.3 45.1 45.7 45.3 weight (g) Ball 2.79 2.80 2.76 2.79 2.82
2.73 2.65 hard- ness (mm) Initial 75.5 75.4 75.4 75.4 75.4 75.5
75.3 velocity (m/s) Scuff 4.4 4.6 4.5 4.6 4.8 3.6 3.1 resist- ance
Feel Excel- Excel- Excel- Excel- Excel- Excel- Good lent lent lent
lent lent lent
[0079] It is evident from Table 4 that inventive golf balls using
cover stocks based on heated mixtures of a thermoplastic
polyurethane elastomer and a functional group-modified polyolefin
are improved in scuff resistance and hitting feel.
[0080] Japanese Patent Application Nos. 311278/1997 and 311279/1997
are incorporated herein by reference.
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