U.S. patent application number 11/647337 was filed with the patent office on 2008-07-03 for golf ball.
This patent application is currently assigned to BRIDGESTONE SPORTS CO., LTD.. Invention is credited to Toshihiko Manami, Eiji Takehana.
Application Number | 20080161128 11/647337 |
Document ID | / |
Family ID | 39584808 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080161128 |
Kind Code |
A1 |
Manami; Toshihiko ; et
al. |
July 3, 2008 |
Golf ball
Abstract
The present invention provides a golf ball comprising a core, an
outermost cover layer and an intermediate layer therebetween. The
intermediate layer is formed primarily of a resin material obtained
by blending together (I) a sodium ion neutralization product of an
olefin-unsaturated carboxylic acid random copolymer with (II) a
magnesium ion neutralization product of an olefin-unsaturated
carboxylic acid random copolymer. The intermediate layer-forming
resin material has a Shore D hardness of from 55 to 70, and the
intermediate layer has a thickness of from 0.5 to 2.5 mm. The
outermost cover layer is formed primarily of a non-ionomeric resin
material. The cover-forming resin material has a Shore D hardness
of from 35 to 60, and the cover has a thickness of from 0.5 to 2.0
mm. The golf ball of the invention has a flight performance and
controllability acceptable for use by professional golfers and
skilled amateurs, and also has an excellent durability to cracking
on repeated impact.
Inventors: |
Manami; Toshihiko;
(Chichibu-shi, JP) ; Takehana; Eiji;
(Chichibu-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
Tokyo
JP
|
Family ID: |
39584808 |
Appl. No.: |
11/647337 |
Filed: |
December 29, 2006 |
Current U.S.
Class: |
473/371 |
Current CPC
Class: |
A63B 37/0031 20130101;
A63B 37/0045 20130101; A63B 37/0038 20130101; A63B 37/0043
20130101; A63B 37/0033 20130101 |
Class at
Publication: |
473/371 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Claims
1. A golf ball comprising a core, an outermost cover layer and an
intermediate layer therebetween, wherein the intermediate layer is
formed primarily of a resin material obtained by blending together
(I) a sodium ion neutralization product of an olefin-unsaturated
carboxylic acid random copolymer with (II) a magnesium ion
neutralization product of an olefin-unsaturated carboxylic acid
random copolymer, the intermediate layer-forming resin material
having a Shore D hardness of from 55 to 70 and the intermediate
layer having a thickness of from 0.5 to 2.5 mm; and the outermost
cover layer is formed primarily of a non-ionomeric resin material,
the cover-forming resin material having a Shore D hardness of from
35 to 60 and the cover having a thickness of from 0.5 to 2.0
mm.
2. The golf ball of claim 1, wherein the intermediate layer-forming
material contains material (I) and material (II) in a mixing ratio
by weight of from 20/80 to 80/20.
3. The golf ball of claim 1, wherein the non-ionomeric resin
material in the outermost cover layer is a thermoplastic
polyurethane elastomer.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to golf ball having a core and
a cover of one or more layer. More specifically, the invention
relates to a golf ball having an excellent rebound and
durability.
[0002] Recently, preferred use has been made of urethane resin
materials in the outermost cover layer. In such urethane balls, to
achieve a lower spin rate and a high rebound, the intermediate
layer located inside the outermost cover layer is often made of an
ionomer resin having a high hardness. Ionomer resins are ionic
copolymers of an olefin such as ethylene with an unsaturated
carboxylic acid such as acrylic acid, methacrylic acid or maleic
acid, in which some of the acidic groups are neutralized with metal
ions such as sodium, lithium, zinc or magnesium. In particular,
ionomer resins have excellent characteristics such as durability
and resilience, and are thus well-suited for use as the base resin
in golf ball cover materials.
[0003] When a sodium ion-neutralized ionomer is used alone as the
intermediate layer material, the ball itself has a good rebound but
an inferior durability. When a zinc ion-neutralized ionomer is used
alone as the intermediate layer material, the converse is true;
that is, the ball itself has a good durability but a poor
rebound.
[0004] JP No. 3257890 describes a golf ball in which a material
obtained by blending a sodium ion-neutralized ionomer with a zinc
ion-neutralized ionomer is used to form the intermediate layer.
[0005] In addition, art relating to materials obtained by blending
magnesium ion-neutralized ionomers with other types of ionomers is
disclosed in JP No. 3810133, International Application WO 97/02318,
International Application WO 97/02319, U.S. Pat. No. 6,130,296,
U.S. Pat. No. 6,712,719 and U.S. Pat. No. 6,746,346.
[0006] However, these prior-art materials are all materials having
blended therein a terpolymer; they are not materials which give the
intermediate layer a high hardness and thus enhance the durability
of the golf ball to cracking on repeated impact and the distance
traveled by the ball.
SUMMARY OF THE INVENTION
[0007] It is therefore an object of the present invention to
provide a golf ball which has a flight performance and
controllability acceptable for use by professional golfers and
skilled amateurs, and which also has an excellent durability to
cracking on repeated impact.
[0008] As a result of extensive investigations on ways of achieving
the above object, the inventor has found that, in a multi-piece
solid golf ball composed of a core encased by a multilayer cover,
when the intermediate layer disposed between the core and the
outermost cover layer is given a high hardness and the outermost
cover layer thereon is made of a non-ionomeric thermoplastic
elastomer such as urethane, in the interest of achieving a golf
ball having a good flight performance and controllability and also
having an improved durability to cracking under repeated impact, it
is effective to optimize the material hardness and the thickness of
the intermediate layer by using an intermediate layer material
composed primarily of a resin material obtained by blending
together (I) a sodium ion neutralization product of an
olefin-unsaturated carboxylic acid random copolymer with (II) a
magnesium ion neutralization product of an olefin-unsaturated
carboxylic acid random copolymer.
[0009] Accordingly, the invention provides the following golf
balls. [0010] [1] A golf ball comprising a core, an outermost cover
layer and an intermediate layer therebetween, wherein the
intermediate layer is formed primarily of a resin material obtained
by blending together (I) a sodium ion neutralization product of an
olefin-unsaturated carboxylic acid random copolymer with (II) a
magnesium ion neutralization product of an olefin-unsaturated
carboxylic acid random copolymer, the intermediate layer-forming
resin material having a Shore D hardness of from 55 to 70 and the
intermediate layer having a thickness of from 0.5 to 2.5 mm; and
the outermost cover layer is formed primarily of a non-ionomeric
resin material, the cover-forming resin material having a Shore D
hardness of from 35 to 60 and the cover having a thickness of from
0.5 to 2.0 mm. [0011] [2] The golf ball of [1], wherein the
intermediate layer-forming material contains material (I) and
material (II) in a mixing ratio by weight of from 20/80 to 80/20.
[0012] [3] The golf ball of [1], wherein the non-ionomeric resin
material in the outermost cover layer is a thermoplastic
polyurethane elastomer.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The invention is described more fully below.
[0014] The golf ball of the invention has a multilayer structure
composed of a core and a plurality of cover layers that encapsulate
the core. In the invention, the encapsulating layers outside of the
core include at least an outermost cover layer and an intermediate
layer.
[0015] The diameter of the core, while not subject to any
particular limitation, is preferably in a range of at least 33.0 mm
but not more than 41.0 mm, more preferably at least 35.0 mm but not
more than 40.0 mm, and most preferably at least 36.0 mm but not
more than 39.0 mm. The core has a deflection (mm) when compressed
under a final load of 1,275 N (130 kgf) from an initial load of 98
N (10 kgf) which, while not subject to any particular limitation,
is preferably set in a range of at least 2.8 mm but not more than
7.0 mm, more preferably at least 3.0 mm but not more than 6.0 mm,
and even more preferably at least 3.2 mm but not more than 5.0 mm.
If the core is harder than the above range in values, the feel of
the golf ball when played may worsen and, particularly on long
shots with a club such as a driver that causes large deformation of
the ball, the spin rate may rise excessively, which may keep the
ball from traveling as far as desired. On the other hand, if the
core is softer than the above range in values, the ball may have a
dead feel on impact and insufficient rebound, as a result of which
it may not travel as far as desired. Moreover, the durability to
cracking under repeated impact may worsen.
[0016] The core in the present invention may be provided with a
hardness difference between the surface and center of the core, in
which case the core surface hardness minus the core center hardness
(JIS-C hardness) is generally from 15 to 36, preferably from 18 to
32, and more preferably from 20 to 30. In this way, the spin rate
of the ball on full shots can be lowered. If the above hardness
difference is too small, the spin rate-lowering effect on shots
with a driver (W#1) may be smaller than desirable, shortening the
distance traveled by the ball.
[0017] The core may be formed using a rubber composition which
includes a co-crosslinking agent, an organic peroxide, an inert
filler and an organosulfur compound. It is preferable to use
polybutadiene as the base rubber in the rubber composition.
[0018] It is desirable for the polybutadiene serving as the rubber
component to have a cis-1,4-bond content on the polymer chain of at
least 60 wt %, preferably at least 80 wt %, more preferably at
least 90 wt %, and most preferably at least 95 wt %. Too low a
cis-1,4-bond content among the bonds on the molecule may result in
a lower resilience.
[0019] Moreover, the polybutadiene has a 1,2-vinyl bond content on
the polymer chain of typically not more than 2%, preferably not
more than 1.7%, and more preferably not more than 1.5%. Too high a
1,2-vinyl bond content may result in a lower resilience.
[0020] To obtain a molded and vulcanized rubber composition of good
resilience, the polybutadiene used in the invention is preferably
one synthesized with a rare-earth catalyst or a Group VIII metal
compound catalyst. Polybutadiene synthesized with a rare-earth
catalyst is especially preferred.
[0021] Such rare-earth catalysts are not subject to any particular
limitation. Exemplary rare-earth catalysts include those made up of
a combination of a lanthanide series rare-earth compound with an
organoaluminum compound, an alumoxane, a halogen-bearing compound
and an optional Lewis base.
[0022] Examples of suitable lanthanide series rare-earth compounds
include halides, carboxylates, alcoholates, thioalcoholates and
amides of atomic number 57 to 71 metals.
[0023] In the practice of the invention, the use of a neodymium
catalyst in which a neodymium compound serves as the lanthanide
series rare-earth compound is particularly advantageous because it
enables a polybutadiene rubber having a high cis-1,4 bond content
and a low 1,2-vinyl bond content to be obtained at an excellent
polymerization activity. Suitable examples of such rare-earth
catalysts include those mentioned in JP-A 11-35633, JP-A 11-164912
and JP-A 2002-293996.
[0024] To enhance the resilience, it is preferable for the
polybutadiene synthesized using the lanthanide series rare-earth
compound catalyst to account for at least 10 wt %, preferably at
least 20 wt %, and more preferably at least 40 wt %, of the rubber
components.
[0025] Rubber components other than the above-described
polybutadiene may be included in the base rubber, insofar as the
objects of the invention are attainable. Illustrative examples of
rubber components other than the above-described polybutadiene
include other polybutadienes, and other diene rubbers, such as
styrene-butadiene rubber, natural rubber, isoprene rubber and
ethylene-propylene-diene rubber.
[0026] Examples of co-crosslinking agents include unsaturated
carboxylic acids and the metal salts of unsaturated carboxylic
acids.
[0027] Specific examples of unsaturated carboxylic acids include
acrylic acid, methacrylic acid, maleic acid and fumaric acid.
Acrylic acid and methacrylic acid are especially preferred.
[0028] The metal salts of unsaturated carboxylic acids, while not
subject to any particular limitation, are exemplified by the
above-mentioned unsaturated carboxylic acids neutralized with a
desired metal ion. Specific examples include the zinc and magnesium
salts of methacrylic acid and acrylic acid. The use of zinc
acrylate is especially preferred.
[0029] The unsaturated carboxylic acid and/or metal salt thereof is
included in an amount, per 100 parts by weight of the base rubber,
of generally at least 10 parts by weight, preferably at least 15
parts by weight, and more preferably at least 20 parts by weight,
but generally not more than 60 parts by weight, preferably not more
than 50 parts by weight, more preferably not more than 45 parts by
weight, and most preferably not more than 40 parts by weight. Too
much may make the core too hard, giving the ball an unpleasant feel
on impact, whereas too little may lower the rebound.
[0030] The organic peroxide may be a commercially available
product, suitable examples of which include Percumyl D (produced by
NOF Corporation), Perhexa 3M and Perhexa C-40 (NOF Corporation),
and Luperco 231XL (Atochem Co.). These may be used singly or as a
combination of two or more thereof.
[0031] The amount of organic peroxide included per 100 parts by
weight of the base rubber is generally at least 0.1 part by weight,
preferably at least 0.3 part by weight, more preferably at least
0.5 part by weight, and most preferably at least 0.7 part by
weight, but generally not more than 5 parts by weight, preferably
not more than 4 parts by weight, more preferably not more than 3
parts by weight, and most preferably not more than 2 parts by
weight. Too much or too little organic peroxide may make it
impossible to achieve a ball having a good feel on impact,
durability and rebound.
[0032] Examples of suitable inert fillers include zinc oxide,
barium sulfate and calcium carbonate. These may be used singly or
as a combination of two or more thereof.
[0033] The amount of inert filler included per 100 parts by weight
of the base rubber is generally at least 1 part by weight, and
preferably at least 5 parts by weight, but generally not more than
50 parts by weight, preferably not more than 45 parts by weight,
more preferably not more than 40 parts by weight, and most
preferably not more than 35 parts by weight. Too much or too little
inert filler may make it impossible to achieve a proper weight and
a good rebound.
[0034] In addition, an antioxidant may be included if necessary.
Illustrative examples of suitable commercial antioxidants include
Nocrac 200, Nocrac NS-6, Nocrac NS-30 (all available from Ouchi
Shinko Chemical Industry Co., Ltd.), and Yoshinox 425 (available
from Yoshitomi Pharmaceutical Industries, Ltd.). These may be used
singly or as a combination of two or more thereof.
[0035] The amount of antioxidant included per 100 parts by weight
of the base rubber is generally 0 or more part by weight,
preferably at least 0.05 part by weight, and more preferably at
least 0.1 part by weight, but generally not more than 3 parts by
weight, preferably not more than 2 parts by weight, more preferably
not more than 1 part by weight, and most preferably not more than
0.5 part by weight. Too much or too little antioxidant may make it
impossible to achieve a good rebound and durability.
[0036] To enhance the rebound of the golf ball and increase its
initial velocity, it is preferable to include within the core an
organosulfur compound.
[0037] No particular limitation is imposed on the organosulfur
compound, provided it improves the rebound of the golf ball.
Exemplary organosulfur compounds include thiophenols,
thionaphthols, halogenated thiophenols, and metal salts thereof.
Specific examples include pentachlorothiophenol,
pentafluorothiophenol, pentabromothiophenol, p-chlorothiophenol,
the zinc salt of pentachlorothiophenol, the zinc salt of
pentafluorothiophenol, the zinc salt of pentabromothiophenol, the
zinc salt of p-chlorothiophenol; and diphenylpolysulfides,
dibenzylpolysulfides, dibenzoylpolysulfides,
dibenzothiazoylpolysulfides and dithiobenzoylpolysulfides having 2
to 4 sulfurs. The zinc salt of pentachlorothiophenol is especially
preferred.
[0038] It is recommended that the amount of the organosulfur
compound included per 100 parts by weight of the base rubber be
generally at least 0.05 part by weight, and preferably at least 0.1
part by weight, but generally not more than 5 parts by weight,
preferably not more than 4 parts by weight, more preferably not
more than 3 parts by weight, and most preferably not more than 2.5
parts by weight. If too much organosulfur compound is included, the
effects of addition may peak so that further addition has no
apparent effect, whereas the use of too little organosulfur
compound may fail to confer the effects of such addition to a
sufficient degree.
[0039] Next, the outermost cover layer in the invention is
described.
[0040] In the present invention, the outermost cover layer is
formed primarily of a non-ionomeric resin. The non-ionomeric
material is preferably a thermoplastic resin selected from among
polyester elastomers, polyamide elastomers, polyurethane elastomers
and mixtures thereof. A polyurethane elastomer is most
preferred.
[0041] The polyurethane elastomer used as the outer cover layer
material is not subject to any particular limitation, although the
use of a thermoplastic polyurethane is preferable in terms of
amenability to mass production. In the present invention, it is
preferable to use a cover molding material (C) composed primarily
of the following components A and B: [0042] (A) a thermoplastic
polyurethane material; and [0043] (B) an isocyanate mixture of
(b-1) an isocyanate compound having at least two isocyanate groups
as functional groups per molecule, dispersed in (b-2) a
thermoplastic resin which is substantially non-reactive with
isocyanate.
[0044] In the practice of the invention, when the outermost cover
layer is made of the above cover molding material (C), a golf ball
having a better feel, controllability, cut resistance, scuff
resistance and durability to cracking on repeated impact can be
obtained.
[0045] Components A, B and C are described below.
(A) Thermoplastic Polyurethane Material
[0046] The thermoplastic polyurethane material has a morphology
which includes soft segments composed of a polymeric polyol
(polymeric glycol) and hard segments composed of a chain extender
and a diisocyanate. The polymeric polyol used as a starting
material may be any that has hitherto been employed in the art
relating to thermoplastic polyurethane materials, without
particular limitation. Exemplary polymeric polyols include
polyester polyols and polyether polyols, although polyether polyols
are better than polyester polyols for synthesizing thermoplastic
polyurethane materials that provide a high rebound resilience and
have excellent low-temperature properties. Suitable polyether
polyols include polytetramethylene glycol and polypropylene glycol.
Polytetramethylene glycol is especially preferred for achieving a
good rebound resilience and good low-temperature properties. The
polymeric polyol has an average molecular weight of preferably
1,000 to 5,000. To synthesize a thermoplastic polyurethane material
having a high rebound resilience, an average molecular weight of
2,000 to 4,000 is especially preferred.
[0047] Preferred chain extenders include those used in the prior
art relating to thermoplastic polyurethane materials. Illustrative,
non-limiting, examples include 1,4-butylene glycol, 1,2-ethylene
glycol, 1,3-butanediol, 1,6-hexanediol, and
2,2-dimethyl-1,3-propanediol. These chain extenders have an average
molecular weight of preferably 20 to 15,000.
[0048] Diisocyanates suitable for use include those employed in the
prior art relating to thermoplastic polyurethane materials.
Illustrative, non-limiting, examples include aromatic diisocyanates
such as 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate
and 2,6-toluene diisocyanate; and aliphatic diisocyanates such as
hexamethylene diisocyanate. Depending on the type of isocyanate
used, the crosslinking reaction during injection molding may be
difficult to control. In the present invention, to ensure stable
reactivity with the subsequently described isocyanate mixture (B),
it is most preferable to use an aromatic diisocyanate, and
specifically 4,4'-diphenylmethane diisocyanate.
[0049] A commercial product may be suitably used as the
above-described thermoplastic polyurethane material. Illustrative
examples include Pandex T-8290, Pandex T-8295 and Pandex T-8260
(all manufactured by DIC Bayer Polymer, Ltd.), and Resamine 2593
and Resamine 2597 (both manufactured by Dainichi Seika Colour &
Chemicals Mfg. Co., Ltd.).
(B) Isocyanate Mixture
[0050] The isocyanate mixture (B) is prepared by dispersing (b-1)
an isocyanate compound having as functional groups at least two
isocyanate groups per molecule in (b-2) a thermoplastic resin that
is substantially non-reactive with isocyanate. Above isocyanate
compound (b-1) is preferably an isocyanate compound used in the
prior art relating to thermoplastic polyurethane materials.
Illustrative, non-limiting, examples include aromatic diisocyanates
such as 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate
and 2,6-toluene diisocyanate; and aliphatic diisocyanates such as
hexamethylene diisocyanate. From the standpoint of reactivity and
work safety, the use of 4,4'-diphenylmethane diisocyanate is most
preferred.
[0051] The thermoplastic resin (b-2) is preferably a resin having a
low water absorption and excellent compatibility with thermoplastic
polyurethane materials. Illustrative, non-limiting, examples of
such resins include polystyrene resins, polyvinyl chloride resins,
ABS resins, polycarbonate resins and polyester elastomers (e.g.,
polyether-ester block copolymers, polyester-ester block
copolymers). From the standpoint of rebound resilience and
strength, the use of a polyester elastomer, particularly a
polyether-ester block copolymer, is especially preferred.
[0052] In the isocyanate mixture (B), it is desirable for the
relative proportions of the thermoplastic resin (b-2) and the
isocyanate compound (b-1), expressed as the weight ratio
(b-2):(b-1), to be from 100:5 to 100:100, and especially from
100:10 to 100:40. If the amount of the isocyanate compound (b-1)
relative to the thermoplastic resin (b-2) is too small, a greater
amount of the isocyanate mixture (B) will have to be added to
achieve an amount of addition sufficient for the crosslinking
reaction with the thermoplastic polyurethane material (A). As a
result, the thermoplastic resin (b-2) will exert a large influence,
compromising the physical properties of the cover-molding material
(C). On the other hand, if the amount of the isocyanate compound
(b-1) relative to the thermoplastic resin (b-2) is too large, the
isocyanate compound (b-1) may cause slippage to occur during
mixing, making preparation of the isocyanate mixture (B)
difficult.
[0053] The isocyanate mixture (B) can be obtained by, for example,
adding the isocyanate compound (b-1) to the thermoplastic resin
(b-2) and thoroughly working together these components at a
temperature of 130 to 250.degree. C. using mixing rolls or a
Banbury mixer, then either pelletizing or cooling and subsequently
grinding. A commercial product such as Crossnate EM30 (made by
Dainichi Seika Colour & Chemicals Mfg. Co., Ltd.) may be
suitably used as the isocyanate mixture (B).
(C) Cover-Molding Material The cover-molding material (C) is
composed primarily of the above-described thermoplastic
polyurethane material (A) and isocyanate mixture (B). The relative
proportion of the thermoplastic polyurethane material (A) to the
isocyanate mixture (B) in the cover-molding material (C), expressed
as the weight ratio (A):(B), is preferably from 100:1 to 100:100,
more preferably from 100:5 to 100:50, and even more preferably from
100:10 to 100:30. If too little isocyanate mixture (B) is included
with respect to the thermoplastic polyurethane material (A), a
sufficient crosslinking effect will not be achieved. On the other
hand, if too much is included, unreacted isocyanate may discolor
the molded material.
[0054] In addition to the above-described ingredients, other
ingredients may be included in the cover-molding material (C). For
example, thermoplastic polymeric materials other than the
thermoplastic polyurethane material may be included; illustrative
examples include polyester elastomers, polyamide elastomers,
ionomer resins, styrene block elastomers, polyethylene and nylon
resins. Thermoplastic polymeric materials other than the
thermoplastic polyurethane material may be included in an amount of
0 to 100 parts by weight, preferably 10 to 75 parts by weight, and
more preferably 10 to 50 parts by weight, per 100 parts by weight
of the thermoplastic polyurethane material serving as the essential
component. The amount of such thermoplastic polymeric materials
used is selected as appropriate for such purposes as adjusting the
hardness of the cover material, improving the rebound, improving
the flow properties, and improving adhesion. If necessary, various
additives such as pigments, dispersants, antioxidants, light
stabilizers, ultraviolet absorbers and parting agents may also be
suitably included in the cover-molding material (C).
[0055] Formation of the cover from the cover-molding material (C)
can be carried out by adding the isocyanate mixture (B) to the
thermoplastic polyurethane material (A) and dry mixing, then using
an injection molding machine to mold the mixture into a cover over
the core. The molding temperature varies with the type of
thermoplastic polyurethane material (A), although molding is
generally carried out within a temperature range of 150 to
250.degree. C.
[0056] Reactions and crosslinking which take place in the golf ball
cover obtained as described above are believed to involve the
reaction of isocyanate groups with hydroxyl groups remaining in the
thermoplastic polyurethane material to form urethane bonds, or the
creation of an allophanate or biuret crosslinked form via a
reaction involving the addition of isocyanate groups to urethane
groups in the thermoplastic polyurethane material. Although the
crosslinking reaction has not yet proceeded to a sufficient degree
immediately after injection molding of the cover-molding material
(C), the crosslinking reaction can be made to proceed further by
carrying out an annealing step after molding, in this way
conferring the golf ball cover with useful characteristics.
"Annealing," as used herein, refers to heat aging the cover at a
constant temperature for a given length of time, or aging the cover
for a fixed period at room temperature.
[0057] In addition to the above resin components, various optional
additives may be included in the above-described resin material for
the outermost cover layer. Such additives include, for example,
pigments, dispersants, antioxidants, ultraviolet absorbers,
ultraviolet stabilizers, parting agents, plasticizers, and
inorganic fillers (e.g., zinc oxide, barium sulfate, titanium
dioxide).
[0058] The outermost cover layer has a thickness which is at least
0.5 mm but not more than 2.0 mm, preferably at least 0.5 mm but not
more than 1.5 mm, and more preferably at least 0.6 mm but not more
than 1.3 mm. Moreover, the outermost cover layer has a hardness
(material hardness) which, expressed as the Shore D hardness, is in
a range of from 35 to 60, preferably 40 to 60, and more preferably
42 to 58. Setting the cover thickness and Shore D hardness outside
of these ranges will worsen the feel of the ball on impact and the
spin performance, and thus make it impossible to achieve the
intended effects of the invention.
[0059] The intermediate layer disposed between the above core and
the above outermost cover layer is described below.
[0060] The intermediate layer has a thickness of at least 0.5 mm
but not more than 2.5 mm, preferably at least 0.8 mm but not more
than 2.2 mm, and more preferably at least 1.5 mm but not more than
2.0 m. Outside of this range, the balance between the spin
performance and initial velocity of the ball will be poor,
resulting in a decrease in the flight performance.
[0061] The surface hardness (Shore D) of the intermediate layer,
i.e., the Shore D hardness at the surface of the sphere composed of
the core enclosed by the intermediate layer, while not subject to
any particular limitation, is preferably at least 60 but not more
than 80, more preferably at least 63 but not more than 77, and even
more preferably at least 67 but not more than 73. At a hardness
lower than the above range, the ball may take on too much spin on
full shots, and may therefore not travel as far as desired.
Moreover, the feel on impact may be too soft. On the other hand, at
a hardness greater than the above range, the spin rate may
decrease, making the ball more difficult to control, the feel of
the ball may become too hard, and the durability of the ball to
cracking on repeated impact may worsen. As used herein, "surface
hardness of the intermediate layer" refers to the hardness at the
surface of the sphere obtained by enclosing the core with the
intermediate layer material, and is determined by such factors as
the hardness of the underlying core and the thickness and hardness
of the intermediate layer, and differs from the hardness of the
intermediate layer material proper. Also, the intermediate layer
must be harder than the surface of the outermost layer.
[0062] In the practice of the invention, it is critical for the
intermediate layer material to be composed primarily of a resin
material obtained by blending together (I) a sodium ion
neutralization product of an olefin-unsaturated carboxylic acid
random copolymer with (II) a magnesium ion neutralization product
of an olefin-unsaturated carboxylic acid random copolymer. The
impact resistance of an ionomer is generally determined by such
factors as the type of cation and the resin hardness. In the
material employed in the present invention, because it is known
that using the sodium ion neutralization product of a random
copolymer in combination with the magnesium ion neutralization
product of a random copolymer enables the impact resistance and
durability of the resulting golf ball to be improved to a greater
extent than using such a sodium ion neutralization product by
itself, above materials (I) and (II) are used in combination.
[0063] It is possible here to additionally blend another resin
material, such as a random terpolymer, together with above resin
materials (I) and (II). The above terpolymer may be suitably
admixed within a range that allows the objects of the invention to
be attained, such as a range of about 0 to 5 parts by weight per
100 parts by weight of the base resin.
[0064] It is preferable to use an .alpha.-olefin as the olefin in
above component (I) or component (II). Illustrative examples of
.alpha.-olefins include ethylene, propylene and 1-butene. Of these,
ethylene is especially preferred. These olefins may be used in
combinations of two or more thereof.
[0065] The unsaturated carboxylic acid in component (I) or
component (II) is preferably an .alpha.,.beta.-unsaturated
carboxylic acid having from 3 to 8 carbons. Illustrative examples
of .alpha.,.beta.-unsaturated carboxylic acids having 3 to 8
carbons include acrylic acid, methacrylic acid, ethacrylic acid,
itaconic acid, maleic acid and fumaric acid. Of these, acrylic acid
and methacrylic acid are preferred. These unsaturated carboxylic
acids may be used in combinations of two or more thereof.
[0066] The unsaturated carboxylic acid content in these copolymers
is preferably from 5 to 20 wt %, both for component (I) and
component (II). If the unsaturated carboxylic acid content is too
low, the intermediate material may have a lower rigidity and
resilience, possibly diminishing the flight performance of the golf
ball. On the other hand, if the unsaturated carboxylic acid content
is too high, the intermediate layer may lack sufficient
flexibility.
[0067] When component (I) and component (II) are used in admixture,
the mixing ratio therebetween by weight, expressed as (I)/(II), is
preferably from 20/80 to 80/20, and more preferably from 25/75 to
75/25.
[0068] The ionomer resin used in the invention may be a commercial
product, illustrative examples of which include Surlyn (produced by
E.I. DuPont de Nemours & Co.) and Himilan (produced by
DuPont-Mitsui Polychemicals Co., Ltd.).
[0069] The intermediate layer material has a Shore D hardness of at
least 55 but not more than 70, and preferably at least 58 but not
more than 65.
[0070] The golf ball of the invention can be manufactured using an
ordinary process such as a known injection molding process to form
on top of one another the respective layers described above--the
core, intermediate layer, and cover. For example, a molded and
vulcanized article composed primarily of the rubber material may be
placed as the core within a particular injection-molding mold,
following which the intermediate layer material may be
injection-molded over the core to give an intermediate spherical
body. The spherical body may then be placed within another
injection-molding mold and the cover material injection-molded over
the spherical body to give a multi-piece golf ball. Alternatively,
the cover may be formed as a layer over the intermediate spherical
body by, for example, placing two half-cups, molded beforehand as
hemispherical shells, around the intermediate spherical body so as
to encase it, then molding under applied heat and pressure.
[0071] Numerous dimples may be formed on the surface of the cover.
The dimples arranged on the cover surface, while not subject to any
particular limitation, number preferably at least 250 but not more
than 500, more preferably at least 280 but not more than 360, and
even more preferably at least 300 but not more than 350. If the
number of dimples is higher than the above range, the ball will
tend to have a low trajectory, which may shorten the distance of
travel. On the other hand, if the number of dimples is too small,
the ball will tend to have a high trajectory, as a result of which
an increased distance may not be achieved.
[0072] Any one or combination of two or more dimple shapes,
including circular shapes, various polygonal shapes, dewdrop shapes
and oval shapes, may be suitably used. If circular dimples are
used, the diameter of the dimples may be set to at least about 2.5
mm but not more than about 6.5 mm, and the depth may be set to at
least 0.08 mm but not more than 0.30 mm.
[0073] To fully manifest the aerodynamic characteristics of the
dimples, the dimple coverage on the spherical surface of the golf
ball, which is the sum of the individual dimple surface areas, each
defined by the border of the flat plane circumscribed by the edge
of the dimple, expressed as a ratio (SR) with respect to the
spherical surface area of the ball were it to be free of dimples,
is preferably at least 60% but not more than 90%. Also, to optimize
the trajectory of the ball, the value V0 obtained by dividing the
spatial volume of each dimple below the flat plane circumscribed by
the edge of that dimple by the volume of a cylinder whose base is
the flat plane and whose height is the maximum depth of the dimple
from the cylinder base is preferably at least 0.35 but not more
than 0.80. In addition, the VR value, which is the sum of the
volumes of individual dimples formed below flat planes
circumscribed by the dimple edges, as a percentage of the volume of
the ball sphere were it to have no dimples thereon, is preferably
at least 0.6% but not more than 1.0%. Outside of the above ranges
for these values, the ball may assume a trajectory that is not
conducive to achieving a good distance, as a result of which the
ball may fail to travel a sufficient distance when played.
[0074] The golf ball of the invention may be manufactured so as to
conform with the Rules of Golf for competitive play. That is, it
may be produced to a ball diameter which is of a size that will not
pass through a ring having an inside diameter of 42.672 mm, but is
not more than 42.80 mm, and to a weight of generally from 45.0 to
45.93 g.
[0075] As explained above, the golf ball of the invention has a
flight performance and controllability acceptable for use by
professional golfers and skilled amateurs, and also has an
excellent durability to cracking on repeated impact.
EXAMPLES
[0076] Examples of the invention and Comparative Examples are given
below by way of illustration, and not by way of limitation.
Examples 1 to 3, Comparative Examples 1 and 2
[0077] Using the core materials composed primarily of polybutadiene
shown in Table 1 below, solid cores having a diameter of 37.3 mm, a
weight of 31.9 g and a deflection (deformation) of 4.1 mm were
produced. The deflection values were measured as the amount of
deformation experienced by the core when it was compressed under a
final load of 1,275 N (130 kgf) from an initial load state of 98 N
(10 kgf).
TABLE-US-00001 TABLE 1 Amount formulated (pbw) Formulation
Polybutadiene (1) 80 Polybutadiene (2) 20 Zinc oxide 21.3 Zinc
stearate 5.0 Zinc salt of 1.5 pentachlorothiophenol Antioxidant 0.1
Zinc acrylate 32.0 Peroxide 3.0 Sulfur 0.1 Specific gravity 1.2
Specifications Diameter (mm) 37.3 Weight (g) 31.9 Deflection (mm)
4.1
[0078] Details concerning the above formulation are given below.
[0079] Butadiene rubber (1): Produced by JSR Corporation under the
trade name BR 730. [0080] Butadiene rubber (2): Produced by JSR
Corporation under the trade name BR 51. [0081] Zinc stearate:
Produced by NOF Corporation under the trade name Zinc Stearate G.
[0082] Antioxidant: Produced by Sumitomo Chemical Co., Ltd. under
the trade name ANTIGENE BH-T. [0083] Peroxide: Dicumyl peroxide.
Produced by NOF Corporation under the trade name Percumyl D.
[0084] Next, an intermediate layer material of the composition
shown in Table 3 was injection-molded to a thickness of 1.67 mm
within a mold in which the above solid core had been placed. The
cover material shown in Table 2 was then injection-molded to a
thickness of 1.01 mm over the intermediate layer material-enclosed
core within another mold, thereby producing a three-piece solid
golf ball having a diameter of 42.7 mm. The intermediate layer
material was prepared by mixture at 200.degree. C. in a
co-rotating, intermeshing twin-screw extruder (screw diameter, 32
mm; L/D=30; main motor output, 7.5 kw; with vacuum vent).
TABLE-US-00002 TABLE 2 Amount formulated (pbw) Formulation T-8295
50 T-8290 50 Titanium oxide 3.8 Polyethylene wax 1.4 Isocyanate
compound 18 Specific gravity 1.01 Weight (g) 5.78 Material hardness
(Shore D hardness) 48
[0085] Details concerning the above formulation are given below.
[0086] T-8290, T-8295: MDI-PTMG type thermoplastic polyurethanes
produced by DIC Bayer Polymer under the trademark designation
Pandex. [0087] Titanium oxide: Produced by Ishihara Sangyo Kaisha,
Ltd. under the trade name Tipaque R550. [0088] Polyethylene wax:
Produced by Sanyo Chemical Industries, Ltd. under the trade name
Sanwax 161P.
Isocyanate Compound:
[0089] Crossnate EM30 (trade name), an isocyanate masterbatch which
is produced by Dainichi Seika Colour & Chemicals Mfg. Co.,
Ltd., contains 30% of 4,4'-diphenylmethane diisocyanate (measured
concentration of amine reverse-titrated isocyanate according to
JIS-K1556, 5 to 10%), and in which the masterbatch base resin is a
polyester elastomer (Hytrel 4001, produced by DuPont-Toray Co.,
Ltd.). The isocyanate compound was mixed at the time of injection
molding.
[0090] Details concerning the above formulation are given below.
[0091] Himilan 1706 (trade name): An ionomer resin which is a zinc
ion-neutralized ethylene-methacrylic acid random copolymer produced
by DuPont-Mitsui Polychemicals Co., Ltd. [0092] Himilan 1605 (trade
name): An ionomer resin which is a sodium ion-neutralized
ethylene-methacrylic acid random copolymer produced by
DuPont-Mitsui Polychemicals Co., Ltd. [0093] AM7311 (trade name):
An ionomer resin which is a magnesium ion-neutralized
ethylene-methacrylic acid random copolymer produced by
DuPont-Mitsui Polychemicals Co., Ltd. [0094] TMP (trade name): A
trimethylolpropane produced by Mitsubishi Gas Chemical Co.,
Ltd.
TABLE-US-00003 [0094] TABLE 3 Comparative Example Example 1 2 3 1 2
Intermediate H1706 (Zn ion type) 100 layer resin H1605 (Na ion
type) 30 50 70 100 formulation AM7311 (Mg ion type) 70 50 30 TMP
1.1 1.1 1.1 1.1 1.1 Resin MFR (190.degree. C., g/10 min) 1.3 1.7
1.5 0.7 2.0 properties Specific gravity 0.94 0.94 0.95 0.96 0.95
Shore D hardness 65 65 66 62 64 Ball Diameter (mm) 42.7 42.7 42.7
42.7 42.7 properties Weight (g) 45.6 45.6 45.6 45.6 45.6 Deflection
hardness (mm) 2.8 2.7 2.7 2.9 2.8 Initial velocity (m/s) 77.0 77.1
77.1 76.6 76.9 Durability to cracking 170 178 171 140 143 on
repeated impact (shot number) Note: Numbers for the intermediate
layer resin formulation are shown as parts by weight.
Evaluation of Cover Material Properties
[0095] Melt Mass Flow Rate:
[0096] The melt mass flow rate of a material measured in accordance
with JIS-K6760 (test temperature, 190.degree. C.; test load, 21 N
(2.16 kgf)). [0097] Cover Resin Hardness:
[0098] The shore D hardness measured in accordance with ASTM D-2240
is shown.
Evaluation of Ball Properties
[0099] Ball Deflection (Deformation) (mm):
[0100] The deformation (mm) of the golf ball when compressed under
a final load of 1,275 N (130 kgf) from an initial load state of 98
N (10 kgf) was determined. [0101] Ball Initial Velocity (m/s):
[0102] The initial velocity (m/s) was measured using an initial
velocity measuring apparatus of the same type as that of the
official golf ball regulating-body--R&A (USGA), and in
accordance with R&A (USGA) rules. [0103] Durability to Repeated
Impact:
[0104] The golf ball was repeatedly struck at a head speed (HS) of
45 m/s, and the durability to repeated impact was rated as the
number of times the ball had been hit when the rebound decreased
successively by 3%. Each value shown in the table is the average
shot number for four balls.
* * * * *