U.S. patent application number 13/568268 was filed with the patent office on 2013-01-31 for multi-piece solid golf ball.
This patent application is currently assigned to BRIDGESTONE SPORTS CO., LTD.. The applicant listed for this patent is Akira KIMURA, Junji UMEZAWA, Hideo WATANABE. Invention is credited to Akira KIMURA, Junji UMEZAWA, Hideo WATANABE.
Application Number | 20130029787 13/568268 |
Document ID | / |
Family ID | 47597662 |
Filed Date | 2013-01-31 |
United States Patent
Application |
20130029787 |
Kind Code |
A1 |
WATANABE; Hideo ; et
al. |
January 31, 2013 |
MULTI-PIECE SOLID GOLF BALL
Abstract
A multi-piece solid golf ball has a core, an envelope layer
encasing the core, an intermediate layer encasing the envelope
layer, and an outer layer which encases the intermediate layer and
has formed on a surface thereof a plurality of dimples. The core is
made of an elastomer. The envelope layer is formed of an inner
envelope layer and an outer envelope layer, and the intermediate
layer is formed of an inner intermediate layer and an outer
intermediate layer. The outer layer has a hardness which is higher
than the average core hardness, and each of the envelope layers and
the intermediate layers is softer than the outer layer.
Inventors: |
WATANABE; Hideo;
(Chichibushi, JP) ; UMEZAWA; Junji; (Chichibushi,
JP) ; KIMURA; Akira; (Chichibushi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WATANABE; Hideo
UMEZAWA; Junji
KIMURA; Akira |
Chichibushi
Chichibushi
Chichibushi |
|
JP
JP
JP |
|
|
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
Tokyo
JP
|
Family ID: |
47597662 |
Appl. No.: |
13/568268 |
Filed: |
August 7, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12971795 |
Dec 17, 2010 |
|
|
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13568268 |
|
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Current U.S.
Class: |
473/373 ;
473/376 |
Current CPC
Class: |
A63B 37/0033 20130101;
A63B 37/0043 20130101; A63B 37/0062 20130101; A63B 37/0031
20130101; A63B 37/0092 20130101; A63B 37/0039 20130101; A63B
37/0064 20130101; A63B 37/0076 20130101; C08L 23/0846 20130101;
A63B 37/0045 20130101 |
Class at
Publication: |
473/373 ;
473/376 |
International
Class: |
A63B 37/06 20060101
A63B037/06; A63B 37/00 20060101 A63B037/00 |
Claims
1. A multi-piece solid golf ball comprising a core, an envelope
layer encasing the core, an intermediate layer encasing the
envelope layer, and an outer layer which encases the intermediate
layer and has formed on a surface thereof a plurality of dimples,
wherein the core is made of an elastomer; the envelope layer is
formed of an inner envelope layer and an outer envelope layer; the
intermediate layer is formed of an inner intermediate layer and an
outer intermediate layer; letting the average hardness of the core
be expressed by the following formula: average core hardness (Shore
D)=[core surface hardness (Shore D)+core center hardness (Shore
D)]/2, the outer layer has a hardness (Shore D) which is higher
than the average core hardness; letting C10 represent a JIS-C
cross-sectional hardness at a position 10 mm from a center of the
core on a cross-section obtained by cutting the core in half and H
represent a JIS-C surface hardness of the core, the hardnesses C10
and H satisfy the condition: 10.ltoreq.(H-C10).ltoreq.30; and each
of the envelope layers and the intermediate layers is softer than
the outer layer.
2. The multi-piece solid golf ball of claim 1, wherein the envelope
layers, the intermediate layers and the outer layer have Shore D
hardnesses which satisfy the following relationship: outer layer
hardness>outer intermediate layer hardness>inner intermediate
layer hardness>outer envelope layer hardness>inner envelope
layer hardness.
3. The multi-piece solid golf ball of claim 1, wherein the core,
the envelope layers, the intermediate layers and the outer layer
have Shore D hardnesses which satisfy the following five
relationships: 3.ltoreq.(outer layer hardness-outer intermediate
layer hardness).ltoreq.20, 1.ltoreq.(outer intermediate layer
hardness-inner intermediate layer hardness).ltoreq.10,
1.ltoreq.(inner intermediate layer hardness-outer envelope layer
hardness).ltoreq.10, 1.ltoreq.(outer envelope layer hardness-inner
envelope layer hardness).ltoreq.10, and 5.ltoreq.(outer layer
hardness-average core hardness).ltoreq.40.
4. The multi-piece solid golf ball of claim 1, wherein the envelope
layers, the intermediate layers and the outer layer have
thicknesses which satisfy the following relationships:
0.1.ltoreq.outer layer thickness/(outer intermediate layer
thickness+inner intermediate layer thickness+outer envelope layer
thickness+inner envelope layer thickness).ltoreq.1, and 1.0
mm.ltoreq.(outer intermediate layer thickness+inner intermediate
layer thickness+outer envelope layer thickness+inner envelope layer
thickness).ltoreq.10 mm.
5. The multi-piece solid golf ball of claim 1, wherein the outer
layer is formed of a material composed primarily of an ionomer, and
the outer layer material includes one or more type of ionomer resin
having an acid content of at least 16 wt %.
6. The multi-piece solid golf ball of claim 1, wherein the core,
envelope layers, intermediate layers and outer layer have Shore D
hardnesses which satisfy the following relationship: outer layer
hardness>outer intermediate layer hardness>inner intermediate
layer hardness>outer envelope layer hardness>inner envelope
layer hardness>core center hardness.
7. The multi-piece solid golf ball of claim 1, wherein the envelope
layers, intermediate layers and outer layer have thicknesses which
satisfy the following relationship: outer layer
thickness.ltoreq.(outer intermediate layer thickness+inner
intermediate layer thickness+outer envelope layer thickness+inner
envelope layer thickness)<core diameter.
8. The multi-piece solid golf ball of claim 1, wherein at least one
layer from among the inner envelope layer, outer envelope layer,
inner intermediate layer and outer intermediate layer is formed of
a material obtained by blending: an ionomer resin component of (a)
an olefin-unsaturated carboxylic acid random copolymer and/or a
metal ion neutralization product of an olefin-unsaturated
carboxylic acid random copolymer mixed with (b) an
olefin-unsaturated carboxylic acid-unsaturated carboxylic acid
ester random terpolymer and/or a metal ion neutralization product
of an olefin-unsaturated carboxylic acid-unsaturated carboxylic
acid ester random terpolymer in a weight ratio between 100:0 and
0:100, and (e) a non-ionomeric thermoplastic elastomer in a weight
ratio between 100:0 and 50:50.
9. The multi-piece solid golf ball of claim 1, wherein at least one
layer from among the inner envelope layer, outer envelope layer,
inner intermediate layer and outer intermediate layer is formed of
a material obtained by blending, as essential ingredients: 100
parts by weight of a resin component composed of, in admixture, a
base resin of (a) an olefin-unsaturated carboxylic acid random
copolymer and/or a metal ion neutralization product of an
olefin-unsaturated carboxylic acid random copolymer mixed with (b)
an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid
ester random terpolymer and/or a metal ion neutralization product
of an olefin-unsaturated carboxylic acid-unsaturated carboxylic
acid ester random terpolymer in a weight ratio between 100:0 and
0:100, and (e) a non-ionomeric thermoplastic elastomer in a weight
ratio between 100:0 and 50:50; (c) from 5 to 120 parts by weight of
a fatty acid and/or fatty acid derivative having a molecular weight
of from 228 to 1500; and (d) from 0.1 to 17 parts by weight of a
basic inorganic metal compound capable of neutralizing
un-neutralized acid groups in the base resin and component (c).
10. The multi-piece solid golf ball of claim 9, wherein at least
two layers from among the inner envelope layer, outer envelope
layer, inner intermediate layer and outer intermediate layer are
formed of the material of claim 9 which is composed of, as
essential ingredients, components (a) to (e).
11. The multi-piece solid golf ball of claim 9, wherein at least
three layers from among the inner envelope layer, outer envelope
layer, inner intermediate layer and outer intermediate layer are
formed of the material of claim 9 which is composed of, as
essential ingredients, components (a) to (e).
12. The multi-piece solid golf ball of claim 9, wherein the inner
envelope layer, outer envelope layer, inner intermediate layer and
outer intermediate layer are all formed of the material of claim 9
which is composed of, as essential ingredients, components (a) to
(e).
13. The multi-piece solid golf ball of claim 1, wherein the core,
envelope layers, intermediate layers and outer layer have
thicknesses which satisfy the following four relationships:
0.75.ltoreq.(outer intermediate layer thickness+inner intermediate
layer thickness)/outer layer thickness.ltoreq.1.5,
0.75.ltoreq.(outer envelope layer thickness+inner envelope layer
thickness)/outer layer thickness.ltoreq.1.5, 0.75.ltoreq.(outer
intermediate layer thickness+inner intermediate layer
thickness)/(outer envelope layer thickness+inner envelope layer
thickness).ltoreq.1.5, and outer layer thickness<(outer
intermediate layer thickness+inner intermediate layer
thickness+outer envelope layer thickness+inner envelope layer
thickness)<core diameter.
14. The multi-piece solid golf ball of claim 1, wherein, letting C0
represent a JIS-C cross-sectional hardness at the center of the
core on a cross-section obtained by cutting the core in half, C4
represent a JIS-C cross-sectional hardness at a position 4 mm from
the center of the core, C10 represent a JIS-C cross-sectional
hardness at a position 10 mm from the center of the core, and H
represent a JIS-C surface hardness of the core, the hardnesses C0,
C4, C10 and H satisfy the conditions: C4-C0.ltoreq.5,
2.ltoreq.C10-C4.ltoreq.12, and C4-C0.ltoreq.C10-C4<H-C10.
15. The multi-piece solid golf ball of claim 1, wherein the core
has a single-layer structure.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of copending
application Ser. No. 12/971,795 filed on Dec. 17, 2010, the entire
contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a multi-piece solid golf
ball composed of a core, an envelope layer, an intermediate layer
and an outer layer that have been formed as successive layers. More
specifically, the invention relates to a multi-piece solid golf
ball which is intended primarily to achieve an excellent flight
when played by an ordinary amateur golfer with a head speed that is
not very high, and to have a good, soft feel on impact.
[0003] Key performance features required in a golf ball include
distance, controllability, durability and feel on impact. Balls
endowed with these qualities in the highest degree are constantly
being sought. Among recent golf balls, there has emerged a
succession of balls which have multilayer structures typically
consisting of three pieces. By having the structure of a golf ball
be multilayered, it is possible to combine numerous materials of
different properties, enabling a wide variety of ball designs in
which each layer has a particular function to be obtained.
[0004] Golf balls which place a premium on distance and a soft feel
have hitherto been widely used primarily as balls for ordinary
amateur golfers. How to design the thickness and hardness of the
respective layers of the ball in such a way as to maximize these
effects is thus a major topic of interest. However, there are
limitations in the design of hardnesses and thicknesses in
two-piece solid golf balls and three-piece solid golf balls. Hence,
numerous disclosures, including those mentioned below, have been
made on multilayer balls having four pieces or five pieces.
[0005] Golf balls with such a multilayer structure have been
disclosed in, for example, JP-A 2009-160407, U.S. Pat. No.
6,302,808, JP-A 2001-017569, JP-A 2001-017570, JP-A 2001-037914,
JP-A 2000-61002, JP-A 2000-60997, JP-A 2000-61000, JP-A 2000-61001,
JP-A 2001-218872, JP-A 2005-218859, JP-A 8-336618 and JP-A
9-56848.
[0006] However, in such prior-art golf balls with a multilayer
structure, because a strong emphasis is often placed on numerous
qualities other than flight, such as the spin rate on approach
shots, the feel on impact and durability, they lack a sufficient
spin rate-lowering effect on full shots, leaving room for further
improvement in the distance traveled by the ball on shots with a
driver.
SUMMARY OF THE INVENTION
[0007] It is therefore an object of the present invention to
provide a multi-piece solid golf ball which is able to achieve an
excellent flight when played by ordinary amateur golfers having
head speeds that are not very high, and which has a good, soft feel
on impact.
[0008] The inventors have conducted extensive investigations in
order to attain the above object. As a result, they have discovered
that, by optimizing the hardness profile at the core interior and
adopting a basic ball construction wherein the layers encasing the
core have a multilayer construction of five or more layers which
includes, in order from the inner side: an inner envelope layer, an
outer envelope layer, an inner intermediate layer, an outer
intermediate layer and an outer layer, by composing the core of an
elastomer, and by designing the ball hardness in such a way that,
when the average hardness in the core is expressed by the following
formula
[0009] average core hardness (Shore D)=[core surface hardness
(Shore D)+core center hardness (Shore D)]/2, the outer layer
hardness (Shore D) is higher than the average core hardness and
each of the envelope layers and the intermediate layers is softer
than the outer layer, the ball can achieve an excellent flight when
played by ordinary amateur golfers having head speeds that are not
very high and can exhibit a good, soft feel on impact. In
particular, it is possible in this invention to further reduce the
spin rate on shots with a driver and thus to achieve a further
increase in distance.
[0010] That is, the multi-piece solid golf ball of the present
invention, by basically having a multilayer construction of six or
more layers in which at least five cover layers are formed over a
core and having the outer layer be relatively hard, is able to
achieve both a low spin rate and a high rebound. In addition, owing
to an exquisite combination of hardnesses and thicknesses among the
respective layers other than the outer layer (i.e., the inner
envelope layer, outer envelope layer, inner intermediate layer and
outer intermediate layer, which layers are collectively referred to
herein as the "inner layers"), the spin rate is reduced and the
rebound is increased on full shots, enabling an excellent distance
to be achieved. Moreover, a good, soft feel can be obtained on full
shots.
[0011] Accordingly, the invention provides the following
multi-piece solid golf ball.
[1] A multi-piece solid golf ball comprising a core, an envelope
layer encasing the core, an intermediate layer encasing the
envelope layer, and an outer layer which encases the intermediate
layer and has formed on a surface thereof a plurality of dimples,
wherein the core is made of an elastomer; the envelope layer is
formed of an inner envelope layer and an outer envelope layer; the
intermediate layer is formed of an inner intermediate layer and an
outer intermediate layer; letting the average hardness of the core
be expressed by the following formula:
[0012] average core hardness (Shore D)=[core surface hardness
(Shore D)+core center hardness (Shore D)]/2, the outer layer has a
hardness (Shore D) which is higher than the average core hardness;
letting C10 represent a JIS-C cross-sectional hardness at a
position 10 mm from a center of the core on a cross-section
obtained by cutting the core in half and H represent a JIS-C
surface hardness of the core, the hardnesses C10 and H satisfy the
condition:
10.ltoreq.(H-C10).ltoreq.30;
and each of the envelope layers and the intermediate layers is
softer than the outer layer. [2] The multi-piece solid golf ball of
[1], wherein the envelope layers, the intermediate layers and the
outer layer have Shore D hardnesses which satisfy the following
relationship:
[0013] outer layer hardness>outer intermediate layer
hardness>inner intermediate layer hardness>outer envelope
layer hardness>inner envelope layer hardness.
[3] The multi-piece solid golf ball of [1], wherein the core, the
envelope layers, the intermediate layers and the outer layer have
Shore D hardnesses which satisfy the following five
relationships:
3.ltoreq.(outer layer hardness-outer intermediate layer
hardness).ltoreq.20,
1.ltoreq.(outer intermediate layer hardness-inner intermediate
layer hardness).ltoreq.10,
1.ltoreq.(inner intermediate layer hardness-outer envelope layer
hardness).ltoreq.10,
1.ltoreq.(outer envelope layer hardness-inner envelope layer
hardness).ltoreq.10, and
5.ltoreq.(outer layer hardness-average core
hardness).ltoreq.40.
[4] The multi-piece solid golf ball of [1], wherein the envelope
layers, the intermediate layers and the outer layer have
thicknesses which satisfy the following relationships:
0.1.ltoreq.outer layer thickness/(outer intermediate layer
thickness+inner intermediate layer thickness+outer envelope layer
thickness+inner envelope layer thickness).ltoreq.1, and
1.0 mm.ltoreq.(outer intermediate layer thickness+inner
intermediate layer thickness+outer envelope layer thickness+inner
envelope layer thickness).ltoreq.10 mm.
[5] The multi-piece solid golf ball of [1], wherein the outer layer
is formed of a material composed primarily of an ionomer, and the
outer layer material includes one or more type of ionomer resin
having an acid content of at least 16 wt %. [6] The multi-piece
solid golf ball of [1], wherein the core, envelope layers,
intermediate layers and outer layer have Shore D hardnesses which
satisfy the following relationship:
outer layer hardness>outer intermediate layer hardness>inner
intermediate layer hardness>outer envelope layer
hardness>inner envelope layer hardness>core center
hardness.
[7] The multi-piece solid golf ball of [1], wherein the envelope
layers, intermediate layers and outer layer have thicknesses which
satisfy the following relationship:
outer layer thickness (outer intermediate layer thickness+inner
intermediate layer thickness+outer envelope layer thickness+inner
envelope layer thickness)<core diameter.
[8] The multi-piece solid golf ball of [1], wherein at least one
layer from among the inner envelope layer, outer envelope layer,
inner intermediate layer and outer intermediate layer is formed of
a material obtained by blending:
[0014] an ionomer resin component of (a) an olefin-unsaturated
carboxylic acid random copolymer and/or a metal ion neutralization
product of an olefin-unsaturated carboxylic acid random copolymer
mixed with (b) an olefin-unsaturated carboxylic acid-unsaturated
carboxylic acid ester random terpolymer and/or a metal ion
neutralization product of an olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester random terpolymer in a
weight ratio between 100:0 and 0:100, and
[0015] (e) a non-ionomeric thermoplastic elastomer in a weight
ratio between 100:0 and 50:50.
[9] The multi-piece solid golf ball of [1], wherein at least one
layer from among the inner envelope layer, outer envelope layer,
inner intermediate layer and outer intermediate layer is formed of
a material obtained by blending, as essential ingredients:
[0016] 100 parts by weight of a resin component composed of, in
admixture, [0017] a base resin of (a) an olefin-unsaturated
carboxylic acid random copolymer and/or a metal ion neutralization
product of an olefin-unsaturated carboxylic acid random copolymer
mixed with (b) an olefin-unsaturated carboxylic acid-unsaturated
carboxylic acid ester random terpolymer and/or a metal ion
neutralization product of an olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester random terpolymer in a
weight ratio between 100:0 and 0:100, and [0018] (e) a
non-ionomeric thermoplastic elastomer in a weight ratio between
100:0 and 50:50;
[0019] (c) from 5 to 120 parts by weight of a fatty acid and/or
fatty acid derivative having a molecular weight of from 228 to
1500; and
[0020] (d) from 0.1 to 17 parts by weight of a basic inorganic
metal compound capable of neutralizing un-neutralized acid groups
in the base resin and component (c).
[10] The multi-piece solid golf ball of [9], wherein at least two
layers from among the inner envelope layer, outer envelope layer,
inner intermediate layer and outer intermediate layer are formed of
the material of [9] which is composed of, as essential ingredients,
components (a) to (e). [11] The multi-piece solid golf ball of [9],
wherein at least three layers from among the inner envelope layer,
outer envelope layer, inner intermediate layer and outer
intermediate layer are formed of the material of [9] which is
composed of, as essential ingredients, components (a) to (e). [12]
The multi-piece solid golf ball of [9], wherein the inner envelope
layer, outer envelope layer, inner intermediate layer and outer
intermediate layer are all formed of the material of [9] which is
composed of, as essential ingredients, components (a) to (e). [13]
The multi-piece solid golf ball of [1], wherein the core, envelope
layers, intermediate layers and outer layer have thicknesses which
satisfy the following four relationships:
0.75.ltoreq.(outer intermediate layer thickness+inner intermediate
layer thickness)/outer layer thickness.ltoreq.1.5,
0.75.ltoreq.(outer envelope layer thickness+inner envelope layer
thickness)/outer layer thickness.ltoreq.1.5,
0.75.ltoreq.(outer intermediate layer thickness+inner intermediate
layer thickness)/(outer envelope layer thickness+inner envelope
layer thickness).ltoreq.1.5, and
outer layer thickness<(outer intermediate layer thickness+inner
intermediate layer thickness+outer envelope layer thickness+inner
envelope layer thickness)<core diameter.
[14] The multi-piece solid golf ball of [1], wherein, letting C0
represent a JIS-C cross-sectional hardness at the center of the
core on a cross-section obtained by cutting the core in half, C4
represent a JIS-C cross-sectional hardness at a position 4 mm from
the center of the core, C10 represent a JIS-C cross-sectional
hardness at a position 10 mm from the center of the core, and H
represent a JIS-C surface hardness of the core, the hardnesses C0,
C4, C10 and H satisfy the conditions:
C4-C0.ltoreq.5,
2.ltoreq.C10-C4.ltoreq.12, and
C4-C0.ltoreq.C10-C4<H-C10.
[15] The multi-piece solid golf ball of [1], wherein the core has a
single-layer structure.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0021] FIG. 1 is a schematic sectional view showing a multi-piece
solid golf ball (six-layer construction) according to the
invention.
[0022] FIG. 2 is a top view showing the dimple pattern used on the
balls in the examples of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The invention is described more fully below.
[0024] The multi-piece solid golf ball of the present invention, as
shown in FIG. 1, is a golf ball G having a core 1, an envelope 2
encasing the core, an intermediate layer 3 encasing the envelope
layer, and an outer layer 4 encasing the intermediate layer. In
addition, the envelope layer 2 is formed of two layers--an inner
envelope layer 2a and an outer envelope layer 2b, and the
intermediate layer 3 is formed of two layers: an inner intermediate
layer 3a and an outer intermediate layer 3b. The outer layer 4
shown in FIG. 1 typically has a large number of dimples formed on
the surface thereof in the manner shown in FIG. 2, although the
dimples are not shown in FIG. 1. The core 1 is not limited to a
single layer, and may be formed of a plurality of two or more
layers.
[0025] In the invention, the core has a diameter which, although
not subject to any particular limitation, is preferably at least 20
mm, more preferably at least 30 mm, and even more preferably at
least 34 mm. The upper limit in the diameter is preferably not more
than 38 mm, more preferably not more than 37 mm, and even more
preferably not more than 36 mm. At a core diameter outside this
range, the ball may have a lower initial velocity and the spin
rate-lowering effect when the ball is hit with a driver may be
inadequate, as a result of which an increased distance may not be
achieved.
[0026] In the practice of the invention, by optimizing the hardness
profile at the interior of the core, an even lower spin rate can be
achieved on shots with a driver, enabling the ball to travel an
increased distance. A detailed description of the hardness profile
at the core interior is provided below.
[0027] First, in the invention, to set the hardnesses at various
places on the interior of the core, let C0 represent a JIS-C
cross-sectional hardness at a center of the core on a cross-section
obtained by cutting the core in half, C2 represent a JIS-C
cross-sectional hardness at a position 2 mm from the core center,
C4 represent a JIS-C cross-sectional hardness at a position 4 mm
from the core center, C6 represent a JIS-C cross-sectional hardness
at a position 6 mm from the core center, C8 represent a JIS-C
cross-sectional hardness at a position 8 mm from the core center,
C10 represent a JIS-C cross-sectional hardness at a position 10 mm
from the core center, C12 represent a JIS-C cross-sectional
hardness at a position 12 mm from the core center, C14 represent a
JIS-C cross-sectional hardness at a position 14 mm from the core
center, C16 represent a JIS-C cross-sectional hardness at a
position 16 mm from the core center, and H represent a JIS-C
surface hardness of the core. The hardnesses at the respective
places on the core cross-section are described in detail below.
[0028] The core surface hardness H, although not subject to any
particular limitation, has a JIS-C hardness of preferably at least
70, more preferably at least 75, and even more preferably at least
80. The upper limit in the JIS-C hardness is preferably not more
than 100, more preferably not more than 95, and even more
preferably not more than 90. The above hardness range, when
expressed as the Shore D hardness, is preferably at least 45, more
preferably at least 49, and even more preferably at least 53. The
upper limit in the Shore D hardness is preferably not more than 68,
more preferably not more than 64, and even more preferably not more
than 60.
[0029] The core center hardness C0, although not subject to any
particular limitation, has a JIS-C hardness of preferably at least
40, more preferably at least 45, and even more preferably at least
50. The upper limit in the JIS-C hardness is preferably not more
than 72, more preferably not more than 68, and even more preferably
not more than 65. The above hardness range, when expressed as the
Shore D hardness, is preferably at least 22, more preferably at
least 26, and even more preferably at least 30. The upper limit in
the Shore D hardness is preferably not more than 47, more
preferably not more than 44, and even more preferably not more than
41.
[0030] The core cross-sectional hardness C2, although not subject
to any particular limitation, has a JIS-C hardness of preferably at
least 55, more preferably at least 57, and even more preferably at
least 60. The upper limit in the JIS-C hardness is preferably not
more than 80, more preferably not more than 70, and even more
preferably not more than 65.
[0031] The core cross-sectional hardness C4, although not subject
to any particular limitation, has a JIS-C hardness of preferably at
least 55, more preferably at least 57, and even more preferably at
least 60. The upper limit in the JIS-C hardness is preferably not
more than 80, more preferably not more than 70, and even more
preferably not more than 65.
[0032] The core cross-sectional hardness C6, although not subject
to any particular limitation, has a JIS-C hardness of preferably at
least 56, more preferably at least 58, and even more preferably at
least 61. The upper limit in the JIS-C hardness is preferably not
more than 81, more preferably not more than 71, and even more
preferably not more than 66.
[0033] The core cross-sectional hardness C8, although not subject
to any particular limitation, has a JIS-C hardness of preferably at
least 58, more preferably at least 60, and even more preferably at
least 63. The upper limit in the JIS-C hardness is preferably not
more than 83, more preferably not more than 73, and even more
preferably not more than 68.
[0034] The core cross-sectional hardness C10, although not subject
to any particular limitation, has a JIS-C hardness of preferably at
least 60, more preferably at least 62, and even more preferably at
least 65. The upper limit in the JIS-C hardness is preferably not
more than 85, more preferably not more than 75, and even more
preferably not more than 70.
[0035] The core cross-sectional hardness C12, although not subject
to any particular limitation, has a JIS-C hardness of preferably at
least 63, more preferably at least 65, and even more preferably at
least 68. The upper limit in the JIS-C hardness is preferably not
more than 88, more preferably not more than 78, and even more
preferably not more than 73.
[0036] The core cross-sectional hardness C14, although not subject
to any particular limitation, has a JIS-C hardness of preferably at
least 71, more preferably at least 73, and even more preferably at
least 76. The upper limit in the JIS-C hardness is preferably not
more than 96, more preferably not more than 86, and even more
preferably not more than 81.
[0037] The core cross-sectional hardness C16, although not subject
to any particular limitation, has a JIS-C hardness of preferably at
least 74, more preferably at least 76, and even more preferably at
least 79. The upper limit in the JIS-C hardness is preferably not
more than 99, more preferably not more than 89, and even more
preferably not more than 84.
[0038] In the invention, it is critical for the hardness difference
H-C10 between the surface hardness H and the cross-sectional
hardness C10 to have a JIS-C hardness value of from 10 to 30. This
hardness difference has a lower limit of preferably at least 13,
and more preferably at least 16, and has an upper limit of
preferably not more than 27, and more preferably not more than 24.
If the hardness difference is too small, the spin rate on shots
with a driver (W#1) may rise, as a result of which a good distance
may not be achieved. On the other hand, if the hardness difference
is too large, the durability of the ball to cracking on repeated
impact may worsen.
[0039] The hardness difference C4-C0 between the cross-sectional
hardness C4 and the center hardness C0, although not subject to any
particular limitation, may be set to a JIS-C hardness value of
preferably not more than 5, more preferably not more than 4, and
even more preferably not more than 3. The lower limit in the JIS-C
hardness value may be set to preferably at least 0. If the hardness
difference is too large or too small, the spin rate on shots with a
driver (W#1) may rise, as a result of which a good distance may not
be achieved.
[0040] The hardness difference C10-C4 between the cross-sectional
hardness C10 and the cross-sectional hardness C4, although not
subject to any particular limitation, may be set to a JIS-C
hardness value of preferably at least 2, and more preferably at
least 3. The upper limit in the JIS-C hardness value may be set to
preferably not more than 12, more preferably not more than 10, and
even more preferably not more than 8. If the hardness difference is
too small, the spin rate on shots with a driver (W#1) may rise, as
a result of which a good distance may not be achieved. On the other
hand, if the hardness difference is too large, the durability of
the ball to cracking on repeated impact may worsen.
[0041] The hardness difference H-C0 between the core center
hardness C0 and the core surface hardness H, although not subject
to any particular limitation, may be set to a JIS-C hardness value
of preferably at least 15, more preferably at least 20, and even
more preferably at least 23. The upper limit in the JIS-C hardness
value may be set to preferably not more than 40, more preferably
not more than 30, and even more preferably not more than 27. If the
hardness difference is too small, the spin rate may become too
high, as a result of which an increased distance may not be
achieved. On the other hand, if the hardness difference is too
large, the durability of the ball to cracking on repeated impact
may worsen or the rebound may decrease, as a result of which an
increased distance may not be achieved.
[0042] Moreover, it is preferable, although not critical, for the
various above hardness differences to satisfy the following
condition:
C4-C0.ltoreq.C10-C4<H-C10.
If the above condition is not satisfied, the spin rate of the ball
on shots with a driver (W#1) may rise, as a result of which a good
distance may not be achieved.
[0043] It is essential for the arithmetic mean of the core surface
hardness H and the core center hardness C0 (i.e., the value
expressed as "(core surface hardness+core center hardness)/2,"
which is referred to below as the "average core hardness") to be
set lower than the subsequently described material hardness of the
outer layer. In this case, the range in the average core hardness,
expressed as the JIS-C hardness, may be set to preferably at least
50, more preferably at least 60, and even more preferably at least
65. The upper limit in the JIS-C hardness is preferably not more
than 95, more preferably not more than 90, and even more preferably
not more than 85. The above hardness range, expressed in terms of
the Shore D hardness, is set to preferably at least 30, more
preferably at least 38, and even more preferably at least 41. The
upper limit is preferably not more than 64, more preferably not
more than 60, and even more preferably not more than 57.
[0044] At an average core hardness below the above ranges, the core
may have an inadequate resilience, as a result of which an
increased distance may not be achieved; also, the feel of the ball
at impact may be too soft, and the durability of the ball to
cracking on repeated impact may worsen. Conversely, at an average
core hardness higher than the above range, the ball may have an
excessively hard feel on full shots and the spin rate may be too
high, as a result of which an increased distance may not be
achieved.
[0045] The core has a deflection when subjected to compressive
loading, i.e., when compressed under a final load of 1,275 N (130
kgf) from an initial load state of 98 N (10 kgf), which, while not
subject to any particular limitation, is preferably at least 2.0
mm, more preferably at least 3.0 mm, and even more preferably at
least 3.4 mm. The upper limit in the core deflection is preferably
not more than 12.0 mm, more preferably not more than 10.0 mm, and
even more preferably not more than 6.0 mm. If this value is too
high, the resilience of the core may become too low, resulting in
an insufficient distance, the feel may become too soft, or the
durability of the ball to cracking on repeated impact may worsen.
On the other hand, if this value is too low, the ball may have an
excessively hard feel on full shots, or the spin rate may be too
high, as a result of which an increased distance may not be
achieved.
[0046] A material composed primarily of rubber material I described
below may be used to form the core having the above-described
surface hardness and deflection.
Rubber Material I
[0047] The rubber material is exemplified by a rubber composition
which contains a base rubber and additionally includes, for
example, a co-crosslinking agent, an organic peroxide, an inert
filler, an organosulfur compound and sulfur. Polybutadiene is
preferably used as the base rubber of this rubber material.
[0048] It is desirable for the polybutadiene 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.
[0049] Also, the polybutadiene has a 1,2-vinyl bond content on the
polymer chain of generally 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.
[0050] To obtain a molded and vulcanized rubber composition having
a 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.
[0051] 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.
[0052] Examples of suitable lanthanide series rare-earth compounds
include halides, carboxylates, alcoholates, thioalcoholates and
amides of atomic number 57 to 71 metals.
[0053] 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.
[0054] To increase 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.
[0055] 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.
[0056] Examples of co-crosslinking agents include unsaturated
carboxylic acids and the metal salts of unsaturated carboxylic
acids.
[0057] Specific examples of unsaturated carboxylic acids include
acrylic acid, methacrylic acid, maleic acid and fumaric acid.
Acrylic acid and methacrylic acid are especially preferred.
[0058] 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.
[0059] The amount of unsaturated carboxylic acid and/or metal salt
thereof included per 100 parts by weight of the base rubber may be
set to preferably at least 4 parts by weight, more preferably at
least 10 parts by weight, and even more preferably at least 20
parts by weight. The upper limit may be set to preferably not more
than 65 parts by weight, more preferably not more than 60 parts by
weight, and even more preferably not more than 45 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.
[0060] The sulfur is not subject to any particular limitation,
although preferred use may be made of a known powdered sulfur or
the like. The amount of the sulfur included per 100 parts by weight
of the base rubber may be set to preferably at least 0.01 part by
weight, more preferably at least 0.03 part by weight, and even more
preferably at least 0.05 part by weight. The upper limit may be set
to preferably not more than 0.3 part by weight, more preferably not
more than 0.2 part by weight, and even more preferably not more
than 0.1 part by weight. At an amount outside of the above range, a
suitable hardness profile at the core interior may not be obtained,
as a result of which the spin rate may rise and a good distance may
not be achieved, in addition to which the durability to cracking on
repeated impact may worsen.
[0061] A known organic peroxide may be used as the organic
peroxide. Illustrative examples include dicumyl peroxide,
1,1-di(t-butylperoxy)cyclohexane, t-butylperoxy laurate, dibenzoyl
peroxide, dilauroyl peroxide and
1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane. These may be
used singly or two or more may be used in combination. Commercial
products may be used as these organic peroxides. Illustrative
examples of such commercial products include those available under
the trade names "Percumyl D," "Perhexa C-40," "Perbutyl L" (all
from NOF Corporation), the trade names "Niper BW" and "Peroyl L"
(both from NOF Corporation), and the trade name "Trigonox 29" (from
Kayaku Akzo Corporation).
[0062] The organic peroxide is included in an amount, per 100 parts
by weight of the base rubber, of preferably at least 0.2 part by
weight, more preferably at least 0.4 part by weight, and even more
preferably at least 0.6 part by weight. The upper limit is
preferably not more than 5 parts by weight, more preferably not
more than 3 parts by weight, and even more preferably not more than
2 parts by weight. At an amount outside of the above range, a
suitable hardness profile at the core interior may not be obtained,
as a result of which the spin rate on shots with a driver (W#1) may
rise and a good distance may not be achieved, in addition to which
the durability to cracking on repeated impact may worsen.
[0063] The compounding ratio based on weight between the above
sulfur and the above organic peroxide (sulfur/organic peroxide),
although not particularly limited, may be set to preferably at
least 0.02, more preferably at least 0.04, and even more preferably
at least 0.06. The upper limit may be set to preferably not more
than 0.5, more preferably not more than 0.3, and even more
preferably not more than 0.2. At a compounding ratio outside of the
above range, a suitable hardness profile may not be obtained, as a
result of which the spin rate on shots with a driver (W#1) may rise
and a good distance may not be achieved, in addition to which the
durability to cracking on repeated impact may worsen.
[0064] Examples of inert fillers that may be advantageously used
include zinc oxide, barium sulfate and calcium carbonate. These may
be used singly or as a combination of two or more thereof.
[0065] The amount of inert filler included per 100 parts by weight
of the base rubber may be set to preferably at least 1 part by
weight, and more preferably at least 5 parts by weight. The upper
limit may be set to preferably not more than 200 parts by weight,
more preferably not more than 150 parts by weight, and even more
preferably not more than 110 parts by weight. Too much or too
little inert filler may make it impossible to achieve a proper
weight and a good rebound.
[0066] In addition, an antioxidant may be included if necessary.
Illustrative examples of suitable commercial antioxidants include
Nocrac NS-6, Nocrac NS-30 (both available from Ouchi Shinko
Chemical Industry Co., Ltd.), and Yoshinox 425 (Yoshitomi
Pharmaceutical Industries, Ltd.). These may be used singly or as a
combination of two or more thereof.
[0067] The amount of antioxidant included may be more than 0, and
is set to preferably at least 0.05 part by weight, and especially
at least 0.1 part by weight, per 100 parts by weight of the base
rubber. The upper limit in the amount of antioxidant may be set to
preferably not more than 3 parts by weight, more preferably not
more than 2 parts by weight, even more preferably not more than 1
part by weight, and most preferably not more than 0.5 part by
weight, per 100 parts by weight of the base rubber. Too much or too
little antioxidant may make it impossible to achieve a good rebound
and durability.
[0068] To enhance the rebound of the golf ball and increase its
initial velocity, it is preferable to include an organosulfur
compound in the base rubber. 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.
[0069] Next, the envelope layer is described.
[0070] In the present invention, as noted above, the envelope layer
encasing the core is formed of two layers: an inner envelope layer
and an outer envelope layer.
[0071] The inner envelope layer has a material hardness, expressed
as the Shore D hardness (measured with a type D durometer in
accordance with ASTM D 2240; the same applies below), which,
although not subject to any particular limitation, is preferably at
least 30, more preferably at least 37, and even more preferably at
least 40. The upper limit in the material hardness of the inner
envelope layer is preferably not more than 56, more preferably not
more than 53, and even more preferably not more than 50. If the
inner envelope layer is too soft, the ball may have too much spin
receptivity on shots with a W#1, as a result of which a good
distance may not be achieved. On the other hand, if the inner
envelope layer is too hard, the ball may have too hard a feel when
played or the ball may have too much spin receptivity on shots with
a W#1, as a result of which a good distance may not be achieved.
The hardness difference between the inner envelope layer and the
adjoining outer envelope layer, expressed in terms of the Shore D
hardness, is preferably at least 1, and more preferably at least 2;
the upper limit is preferably not more than 10, more preferably not
more than 8, and even more preferably not more than 5. Outside of
the above range, the ball may have too much spin receptivity on
full shots, as a result of which a good distance may not be
achieved. Also, the durability to cracking on repeated impact may
worsen.
[0072] As used herein, "material hardness" refers to, in cases
where the material is a resin, the measured hardness of a 2 mm
thick sheet produced by molding the resin composition under applied
pressure. In cases where the material is a rubber, the "material
hardness" refers to the measured hardness of a pressed sheet having
a thickness of about 2 mm produced by loading the rubber
composition into a sheet-forming mold and hot molding at
170.degree. C. for 15 minutes (the same applies below).
[0073] The inner envelope layer has a thickness which, although not
subject to any particular limitation, is preferably at least 0.2
mm, more preferably at least 0.3 mm, and even more preferably at
least 0.5 mm. The upper limit in the thickness of the inner
envelope layer is preferably not more than 2.0 mm, more preferably
not more than 1.5 mm, and even more preferably not more than 1.0
mm. At an inner envelope layer thickness outside this range, the
spin rate-lowering effect on shots with a driver (W#1) may be
inadequate, as a result of which an increased distance may not be
achieved.
[0074] The outer envelope layer has a material hardness, expressed
as the Shore D hardness, which, while not subject to any particular
limitation, is preferably at least 37, more preferably at least 40,
and even more preferably at least 43. The upper limit in the
material hardness of the outer envelope layer is preferably not
more than 58, more preferably not more than 55, and even more
preferably not more than 52. If the outer envelope layer is too
soft, the ball may have too much spin receptivity on shots with a
W#1, as a result of which a good distance may not be achieved. On
the other hand, if the outer envelope layer is too hard, the ball
may have too hard a feel when played or the ball may have too much
spin receptivity on shots with a W#1, as a result of which a good
distance may not be achieved. The hardness difference between the
outer envelope layer and the adjoining inner intermediate layer,
expressed in terms of the Shore D hardness, is preferably at least
1, more preferably at least 2, and even more preferably at least 3;
the upper limit is preferably not more than 10, more preferably not
more than 8, and even more preferably not more than 6. Outside of
the above range in the hardness difference, the ball may have too
much spin receptivity on full shots, as a result of which a good
distance may not be achieved. Also, the durability to cracking on
repeated impact may worsen.
[0075] The outer envelope layer has a thickness which, although not
subject to any particular limitation, is preferably at least 0.2
mm, more preferably at least 0.3 mm, and even more preferably at
least 0.5 mm. The upper limit in thickness is preferably not more
than 2.0 mm, more preferably not more than 1.5 mm, and even more
preferably not more than 1.0 mm. At an outer envelope layer
thickness outside this range, the spin rate-lowering effect on
shots with a driver (W#1) may be inadequate, as a result of which a
good distance may not be achieved.
[0076] In the present invention, the envelope layer is composed of
two layers--an inner envelope layer and an outer envelope layer,
which respective layers may be made of the same or mutually
differing resin materials. The materials which form these envelope
layers may be, for example, rubber materials or resin materials,
and are not subject to any particular limitation. However, in this
invention, preferred use may be made of a material which includes
as an essential component a base resin composed of, in admixture,
specific amounts of (a) an olefin-unsaturated carboxylic acid
random copolymer and/or a metal ion neutralization product of an
olefin-unsaturated carboxylic acid random copolymer and (b) an
olefin-unsaturated carboxylic acid-unsaturated carboxylic acid
ester random terpolymer and/or a metal ion neutralization product
of an olefin-unsaturated carboxylic acid-unsaturated carboxylic
acid ester random terpolymer. In the invention, by using this
material to form at least one of the envelope layers, the spin rate
on shots with a driver (W#1) can be lowered, enabling a longer
distance to be achieved. This material is described in detail
below.
[0077] The olefin in the base resin, whether in component (a) or
component (b), has a number of carbons which is generally at least
2 but not more than 8, and preferably not more than 6. Specific
examples include ethylene, propylene, butene, pentene, hexene,
heptene and octene. Ethylene is especially preferred.
[0078] Examples of unsaturated carboxylic acids include acrylic
acid, methacrylic acid, maleic acid and fumaric acid. Acrylic acid
and methacrylic acid are especially preferred.
[0079] Moreover, the unsaturated carboxylic acid ester is
preferably a lower alkyl ester of the above unsaturated carboxylic
acid. Specific examples include methyl methacrylate, ethyl
methacrylate, propyl methacrylate, butyl methacrylate, methyl
acrylate, ethyl acrylate, propyl acrylate and butyl acrylate. Butyl
acrylate (n-butyl acrylate, i-butyl acrylate) is especially
preferred.
[0080] The olefin-unsaturated carboxylic acid random copolymer of
component (a) and the olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester random terpolymer of
component (b) (the copolymers in components (a) and (b) are
referred to collectively below as "random copolymers") can each be
obtained by random copolymerization of the above components using a
known method.
[0081] It is recommended that the above random copolymers have
unsaturated carboxylic acid contents (acid contents) which are
regulated. Here the content of unsaturated carboxylic acid present
in the random copolymer serving as component (a), although not
subject to any particular limitation, may be set to preferably at
least 4 wt %, more preferably at least 6 wt %, even more preferably
at least 8 wt %, and most preferably at least 10 wt %. Also, it is
recommended that the upper limit be preferably not more than 30 wt
%, more preferably not more than 20 wt %, even more preferably not
more than 18 wt %, and most preferably not more than 15 wt %.
[0082] Similarly, the content of unsaturated carboxylic acid
present in the random copolymer serving as component (b), although
not subject to any particular limitation, may be set to preferably
at least 4 wt %, more preferably at least 6 wt %, and even more
preferably at least 8 wt %. Also, it is recommended that the upper
limit be preferably not more than 15 wt %, more preferably not more
than 12 wt %, and even more preferably not more than 10 wt %. If
the acid content of the random copolymer is too low, the resilience
may decrease, whereas if it is too high, the processability may
decrease.
[0083] The metal ion neutralization products of the random
copolymers of components (a) and (b) may be obtained by
neutralizing some of the acid groups on the random copolymer with
metal ions. Here, specific examples of metal ions for neutralizing
the acid groups include Na.sup.+, K.sup.+, Li.sup.+, Zn.sup.++,
Cu.sup.++, Mg.sup.++, Ca.sup.++, Co.sup.++, Ni.sup.++ and
Pb.sup.++. Of these, preferred use can be made of, for example,
Na.sup.+, Li.sup.+, Zn.sup.++ and Mg.sup.++. Moreover, from the
standpoint of improving resilience, the use of Na.sup.+ is
recommended. The degree of neutralization of the random copolymer
by these metal ions is not subject to any particular limitation.
Such neutralization products may be obtained by a known method. For
example, use may be made of a method in which the random copolymer
is neutralized with a compound such as a formate, acetate, nitrate,
carbonate, bicarbonate, oxide, hydroxide or alkoxide of the
above-mentioned metal ions.
[0084] Sodium ion-neutralized ionomer resins and zinc
ion-neutralized ionomer resins may be suitably used as the above
metal ion neutralization products of the random copolymers to
increase the melt flow rate (MFR) of the material. In this way,
adjustment of the material to the subsequently described optimal
melt flow rate is easy, enabling the moldability to be
improved.
[0085] Commercially available products may be used as above
components (a) and (b). Illustrative examples of the random
copolymer in component (a) include Nucrel N1560, Nucrel N1214,
Nucrel N1035 and Nucrel AN4221C (all products of DuPont-Mitsui
Polychemicals Co., Ltd.), and Escor 5200, Escor 5100 and Escor 5000
(all products of ExxonMobil Chemical). Illustrative examples of the
random copolymer in component (b) include Nucrel AN4311, Nucrel
AN4318 and Nucrel AN4319 (all products of DuPont-Mitsui
Polychemicals Co., Ltd.), and Escor ATX325, Escor ATX320 and Escor
ATX310 (all products of ExxonMobil Chemical).
[0086] Illustrative examples of the metal ion neutralization
product of the random copolymer in component (a) include Himilan
1554, Himilan 1557, Himilan 1601, Himilan 1605, Himilan 1706,
Himilan 1707 and Himilan AM7311 (all products of DuPont-Mitsui
Polychemicals Co., Ltd.), Surlyn 7930 (E.I. DuPont de Nemours &
Co.), and Iotek 3110 and Iotek 4200 (both products of ExxonMobil
Chemical). Illustrative examples of the metal ion neutralization
product of the random copolymer in component (b) include Himilan
1855, Himilan 1856 and Himilan AM7316 (all products of
DuPont-Mitsui Polychemicals Co., Ltd.), Surlyn 6320, Surlyn 8320,
Surlyn 9320 and Surlyn 8120 (all products of E.I. DuPont de Nemours
& Co.), and Iotek 7510 and Iotek 7520 (both products of
ExxonMobil Chemical).
[0087] When preparing the above-described base resin, component (a)
and component (b) are admixed in a weight ratio of generally
between 100:0 and 0:100, preferably between 75:25 and 0:100, more
preferably between 50:50 and 0:100, even more preferably between
25:75 and 0:100, and most preferably 0:100. If too little component
(a) is included, the molded material obtained therefrom may have a
decreased resilience.
[0088] The processability of the base resin can be further improved
by, in addition to adjusting the above mixing ratio, also adjusting
the mixing ratio between the random copolymers and the metal ion
neutralization products of the random copolymers. In this case, it
is recommended that the weight ratio of the random copolymers to
the metal ion neutralization products of the random copolymers be
set to generally between 100:0 and 40:60, preferably between 100:0
and 60:40, more preferably between 100:0 and 80:20, and even more
preferably 100:0. The addition of too much random copolymer may
lower the uniformity of the pellet composition.
[0089] A non-ionomeric thermoplastic elastomer (e) may be included
in the base resin so as to enhance even further both the feel of
the ball on impact and the rebound. Examples of this component (e)
include olefin elastomers, styrene elastomers, polyester
elastomers, urethane elastomers and polyamide elastomers. In this
invention, to further increase the rebound, it is preferable to use
a polyester elastomer or an olefin elastomer. The use of an olefin
elastomer composed of a thermoplastic block copolymer which
includes crystalline polyethylene blocks as the hard segments is
especially preferred.
[0090] A commercially available product may be used as component
(e). Illustrative examples include Dynaron (JSR Corporation) and
the polyester elastomer Hytrel (DuPont-Toray Co., Ltd.).
[0091] Component (e) may be included in an amount of more than 0.
The upper limit in the amount included per 100 parts by weight of
the base resin is preferably not more than 50 parts by weight, more
preferably not more than 40 parts by weight, even more preferably
not more than 30 parts by weight, and most preferably not more than
20 parts by weight. Too much component (e) may lower the
compatibility of the mixture, possibly resulting in a substantial
decline in the durability of the golf ball.
[0092] Next, a fatty acid or fatty acid derivative having a
molecular weight of at least 228 but not more than 1500 may be
added as component (c) to the base resin. Compared with the base
resin, this component (c) has a very low molecular weight and, by
suitably adjusting the melt viscosity of the mixture, helps in
particular to improve the flow properties. Moreover, component (c)
includes a relatively high content of acid groups (or derivatives
thereof), and is capable of suppressing an excessive loss of
resilience.
[0093] The molecular weight of the fatty acid or fatty acid
derivative of component (c) may be set to at least 228, preferably
at least 256, more preferably at least 280, and even more
preferably at least 300. The upper limit may be set to not more
than 1500, preferably not more than 1000, more preferably not more
than 600, and even more preferably not more than 500. If the
molecular weight is too low, the heat resistance cannot be
improved. On the other hand, if the molecular weight is too high,
the flow properties cannot be improved.
[0094] Preferred use as the fatty acid or fatty acid derivative of
component (c) may likewise be made of, for example, an unsaturated
fatty acid (or derivative thereof) containing a double bond or
triple bond on the alkyl moiety, or a saturated fatty acid (or
derivative thereof) in which the bonds on the alkyl moiety are all
single bonds. In either case, it is recommended that the number of
carbons on the molecule be preferably at least 18, more preferably
at least 20, even more preferably at least 22, and most preferably
at least 24. It is recommended that the upper limit be preferably
not more than 80, more preferably not more than 60, even more
preferably not more than 40, and most preferably not more than 30.
Too few carbons may make it impossible to improve the heat
resistance and may also make the acid group content so high as to
diminish the flow-improving effect on account of interactions with
acid groups present in the base resin. On the other hand, too many
carbons increases the molecular weight, which may keep a distinct
flow-improving effect from appearing.
[0095] Specific examples of the fatty acid of component (c) include
myristic acid, palmitic acid, stearic acid, 12-hydroxystearic acid,
behenic acid, oleic acid, linoleic acid, linolenic acid, arachidic
acid and lignoceric acid. Preferred use may be made of stearic
acid, arachidic acid, behenic acid and lignoceric acid in
particular.
[0096] The fatty acid derivative of component (c) is exemplified by
metallic soaps in which the proton on the acid group of the fatty
acid has been replaced with a metal ion. Examples of the metal ion
include Na.sup.+, Li.sup.+, Ca.sup.++, Mg.sup.++, Zn.sup.++,
Mn.sup.++, Al.sup.+++, Ni.sup.++, Fe.sup.++, Fe.sup.+++, Cu.sup.++,
Sn.sup.++, Pb.sup.++ and Co.sup.++. Of these, Ca.sup.++, Mg.sup.++,
and Zn.sup.++, are especially preferred.
[0097] Specific examples of fatty acid derivatives that may be used
as component (c) include magnesium stearate, calcium stearate, zinc
stearate, magnesium 12-hydroxystearate, calcium 12-hydroxystearate,
zinc 12-hydroxystearate, magnesium arachidate, calcium arachidate,
zinc arachidate, magnesium behenate, calcium behenate, zinc
behenate, magnesium lignocerate, calcium lignocerate and zinc
lignocerate. Of these, magnesium stearate, calcium stearate, zinc
stearate, magnesium arachidate, calcium arachidate, zinc
arachidate, magnesium behenate, calcium behenate, zinc behenate,
magnesium lignocerate, calcium lignocerate and zinc lignocerate are
preferred.
[0098] Use may also be made of known metallic soap-modified
ionomers (see, for example, U.S. Pat. No. 5,312,857, U.S. Pat. No.
5,306,760 and International Disclosure WO 98/46671) when using
above-described components (a) and/or (b), and component (c).
[0099] The amount of component (c) included per 100 parts by weight
of the resin component when above components (a), (b) and (e) have
been suitably mixed may be set to at least 5 parts by weight,
preferably at least 10 parts by weight, more preferably at least 20
parts by weight, and even more preferably at least 30 parts by
weight. The upper limit in the amount included may be set to not
more than 120 parts by weight, preferably not more than 115 parts
by weight, more preferably not more than 110 parts by weight, and
even more preferably not more than 100 parts by weight. If the
amount of component (c) included is too small, the melt viscosity
may decrease, lowering the processability. On the other hand, if
the amount included is too large, the durability may decrease.
[0100] A basic inorganic metal compound capable of neutralizing
acid groups in the base resin and in component (c) may be added as
component (d). In cases where this component (d) is not included
and a metal soap-modified ionomer resin (e.g., any of the metal
soap-modified ionomer resins cited in the above-mentioned patent
publications) is used alone, the metallic soap and un-neutralized
acid groups present on the ionomer resin undergo exchange reactions
during mixture under heating, generating a large amount of fatty
acid. Because the fatty acid has a low thermal stability and
readily vaporizes during molding, it may cause molding defects.
Moreover, if the fatty acid deposits on the surface of the molded
material, it may substantially lower paint film adhesion or have
other undesirable effects such as lowering the resilience of the
resulting molded material.
##STR00001##
[0101] To solve this problem, component (d), a basic inorganic
metal compound which neutralizes the acid groups present in the
base resin and component (c), is included as an essential
component. By including component (d), the acid groups in the base
resin and component (c) are neutralized. Moreover, synergistic
effects from the blending of these respective components confer the
resin composition with a number of excellent properties; namely,
the resin composition has a higher thermal stability and at the
same time is imparted with a good moldability, and the resilience
as a golf ball-forming material is enhanced.
[0102] Illustrative examples of the metal ions used here in the
basic inorganic metal compound include Li.sup.+, Na.sup.+, K.sup.+,
Ca.sup.++, Mg.sup.++, Zn.sup.++, Al.sup.+++, Ni.sup.++, Fe.sup.++,
Fe.sup.+++, Cu.sup.++, Mn.sup.++, Sn.sup.++, Pb.sup.++ and
Co.sup.++. Known basic inorganic fillers containing these metal
ions may be used as the basic inorganic metal compound. Specific
examples include magnesium oxide, magnesium hydroxide, magnesium
carbonate, zinc oxide, sodium hydroxide, sodium carbonate, calcium
oxide, calcium hydroxide, lithium hydroxide and lithium carbonate.
In particular, a hydroxide or a monoxide is recommended. Calcium
hydroxide and magnesium oxide, which have a high reactivity with
the base resin, are more preferred. Magnesium oxide is especially
preferred.
[0103] The amount of component (d) included per 100 parts by weight
of the resin component may be set to at least 0.1 part by weight,
preferably at least 0.5 part by weight, more preferably at least 1
part by weight, and even more preferably at least 1.2 parts by
weight. The upper limit in the amount included may be set to not
more than 17 parts by weight, preferably not more than 15 parts by
weight, more preferably not more than 10 parts by weight, and even
more preferably not more than 5 parts by weight. Too little
component (d) may fail to improve thermal stability and resilience,
whereas too much may instead lower the heat resistance of the golf
ball-forming material due to the presence of excess basic inorganic
metal compound.
[0104] By blending specific respective amounts of components (c)
and (d) with the resin component, i.e., the base resin containing
specific respective amounts of components (a) and (b) in admixture
with optional component (e), a material having excellent thermal
stability, flow properties and moldability can be obtained, in
addition to which the resilience of moldings obtained therefrom can
be markedly improved.
[0105] It is recommended that the material formulated from specific
amounts of the above-described resin component and components (c)
and (d) have a high degree of neutralization (i.e., that the
material be highly neutralized). Specifically, it is recommended
that at least 50 mol %, preferably at least 60 mol %, more
preferably at least 70 mol %, and even more preferably at least 80
mol %, of the acid groups in the material be neutralized. Highly
neutralizing the acid groups in the material makes it possible to
more reliably suppress the exchange reactions that cause trouble
when only a base resin and a fatty acid or fatty acid derivative
are used as in the above-cited prior art, thus preventing the
generation of fatty acid. As a result, the thermal stability is
substantially improved and the processability is good, making it
possible to obtain molded products of much better resilience than
prior-art ionomer resins.
[0106] "Degree of neutralization," as used here, refers to the
degree of neutralization of acid groups present within the mixture
of the base resin and the fatty acid or fatty acid derivative
serving as component (c), and differs from the degree of
neutralization of the ionomer resin itself when an ionomer resin is
used as the metal ion neutralization product of a random copolymer
in the base resin. When a mixture of the invention having a certain
degree of neutralization is compared with an ionomer resin alone
having the same degree of neutralization, because the material of
the invention contains a very large number of metal ions owing to
the inclusion of component (d), the density of ionic crosslinks
which contribute to improved resilience is increased, making it
possible to confer the molded product with an excellent
resilience.
[0107] The resin material should preferably have a melt flow rate
(MFR) adjusted within a specific range in order to ensure flow
properties that are particularly suitable for injection molding,
and thus improve moldability. In this case, it is recommended that
the melt flow rate, as measured in accordance with JIS-K7210 at a
temperature of 190.degree. C. and under a load of 21.18 N (2.16
kgf), be adjusted to preferably at least 0.6 g/10 min, more
preferably at least 0.7 g/10 min, even more preferably at least 0.8
g/10 min, and most preferably at least 2 g/10 min. It is
recommended that the upper limit be adjusted to preferably not more
than 20 g/10 min, more preferably not more than 10 g/10 min, even
more preferably not more than 5 g/10 min, and most preferably not
more than 3 g/10 min. Too high or low a melt flow rate may result
in a substantial decline in processability.
[0108] Commercial products may be used as the envelope
layer-forming materials. Specific examples include those having the
trade names HPF 1000, HPF 2000, HPF AD1027, HPF AD1035 and HPF
AD1040, as well as the experimental material HPF SEP1264-3, all
produced by E.I. DuPont de Nemours & Co.
[0109] Next, the intermediate layer is described.
[0110] In the present invention, as mentioned above, the
intermediate layer is composed of two layers: an inner intermediate
layer and an outer intermediate layer.
[0111] The inner intermediate layer has a material hardness,
expressed as the Shore D hardness, which, while not subject to any
particular limitation, is preferably at least 40, more preferably
at least 43, and even more preferably at least 46. The upper limit
is preferably not more than 60, more preferably not more than 58,
and even more preferably not more than 55. If the inner
intermediate layer is too soft, the ball may have excessive spin
receptivity on shots with a W#1, as a result of which a good
distance may not be achieved. On the other hand, if the inner
intermediate layer is too hard, the ball may have too hard a feel
when played or the ball may have too much spin receptivity on shots
with a W#1, as a result of which a good distance may not be
achieved. The hardness difference between the inner intermediate
layer and the adjoining outer intermediate layer, expressed in
terms of the Shore D hardness, is preferably at least 1, more
preferably at least 2, and even more preferably at least 3; the
upper limit is preferably not more than 10, more preferably not
more than 8, and even more preferably not more than 6. Outside of
the above range, the ball may have too much spin receptivity on
full shots, as a result of which a good distance may not be
achieved. Also, the durability to cracking on repeated impact may
worsen.
[0112] The inner intermediate layer has a thickness which, although
not subject to any particular limitation, is preferably at least
0.2 mm, more preferably at least 0.3 mm, and even more preferably
at least 0.5 mm. The upper limit is preferably not more than 2.0
mm, more preferably not more than 1.5 mm, and even more preferably
not more than 1.0 mm. At an inner intermediate layer thickness
outside of this range, the spin rate-lowering effect on shots with
a driver (W#1) may be inadequate, as a result of which an increased
distance may not be achieved.
[0113] The outer intermediate layer has a material hardness,
expressed as the Shore D hardness, which, while not subject to any
particular limitation, is preferably at least 44, more preferably
at least 47, and even more preferably at least 50. The upper limit
is preferably not more than 65, more preferably not more than 61,
and even more preferably not more than 58. If this layer is too
much softer than the above range, the ball may have excessive spin
receptivity on shots with a W#1, as a result of which a good
distance may not be achieved. If this layer is too much harder than
the above range, the ball may have too hard a feel when played or
the ball may have too much spin receptivity on shots with a W#1, as
a result of which a good distance may not be achieved. The hardness
difference between the outer intermediate layer and the adjoining
outer layer, expressed in terms of the Shore D hardness, is
preferably at least 3, more preferably at least 5, and even more
preferably at least 8; the upper limit is preferably not more than
20, more preferably not more than 15, and even more preferably not
more than 12. If this hardness difference is outside of the above
range, the ball may have too much spin receptivity on full shots,
as a result of which a good distance may not be achieved. Also, the
durability to cracking on repeated impact may worsen.
[0114] The outer intermediate layer has a thickness which, although
not subject to any particular limitation, is preferably at least
0.2 mm, more preferably at least 0.3 mm, and even more preferably
at least 0.5 mm. The upper limit is preferably not more than 2.0
mm, more preferably not more than 1.5 mm, and even more preferably
not more than 1.0 mm. At an outer intermediate layer thickness
outside this range, the spin rate-lowering effect on shots with a
driver (W#1) may be inadequate, as a result of which a good
distance may not be achieved.
[0115] No particular limitation is imposed on the resin material
which may be used in the outer and inner intermediate layers,
although it is advantageous to employ the above-described envelope
layer materials.
[0116] Commonly used additives, such as pigments, fillers for
adjusting the specific gravity, dispersants, antioxidants,
ultraviolet absorbers and light stabilizers, may be suitably added
and blended into the above intermediate layer-forming
materials.
[0117] Next, the outer layer is described. As used herein, the term
"outer layer" denotes the cover layer positioned on the outermost
side within the ball construction, and excludes what are referred
to herein as the intermediate layer and the envelope layer.
[0118] The outer layer has a material hardness, expressed as the
Shore D hardness, which, while not subject to any particular
limitation, may be set to preferably at least 55, more preferably
at least 60, and even more preferably at least 63. The upper limit
may be set to preferably not more than 75, more preferably not more
than 70, and even more preferably not more than 68. If the material
hardness of the outer layer is lower than the above range, the ball
may have too much spin receptivity on full shots, as a result of
which a good distance may not be achieved. On the other hand, if
the material hardness of the outer layer is higher than the above
range, the durability of the ball to cracking on repeated impact
may worsen or the ball may have too hard a feel when played with a
putter and on short approach shots.
[0119] The outer layer has a thickness which, while not subject to
any particular limitation, may be set to preferably at least 0.5
mm, more preferably at least 0.9 mm, and even more preferably at
least 1.0 mm. The upper limit may be set to preferably not more
than 2.5 mm, more preferably not more than 2.0 mm, and even more
preferably not more than 1.4 mm. If the outer layer is thicker than
the above range, the ball may have an inadequate rebound on shots
with a driver (W#1) or the spin rate may be too high, as a result
of which an increased distance may not be achieved. On the other
hand, if the outer layer is thinner than the above range, the ball
may have a poor scuff resistance or may have inadequate
controllability even when played by a professional or other skilled
golfer.
[0120] The outer layer may be formed to a thickness similar to that
of the adjoining outer intermediate layer, although it is
preferable for the outer layer to be formed so as to be thicker
than the adjoining outer intermediate layer by an amount within a
range of up to 1.0 mm. If the outer layer is too much thinner than
the outer intermediate layer, the durability of the ball to
cracking on repeated impact may worsen, or the spin rate-lowering
effect on shots with a W#1 may be inadequate, as a result of which
a good distance may not be achieved. On the other hand, if the
outer layer is too much thicker than the outer intermediate layer,
the feel on impact may be too hard or the spin rate-lowering effect
on shots with a W#1 may be inadequate, as a result of which a good
distance may not be achieved.
[0121] The material used in the outer layer of the invention is not
subject to any particular limitation. However, the use of ionomer
resins is most preferred on account of their high rigidity and high
resilience. Such ionomer resins are exemplified by, in particular,
ionomer resins in which some of the carboxylic acids in a copolymer
of an .alpha.-olefin and an .alpha.,.beta.-unsaturated carboxylic
acid of 3 to 8 carbons are neutralized with metal ions, ionomer
resins in which at least some of the carboxylic acids in a
terpolymer of an .alpha.-olefin, an .alpha.,.beta.-unsaturated
carboxylic acid of 3 to 8 carbons and an .alpha.,.beta.-unsaturated
carboxylic acid ester are neutralized with metal ions, and mixtures
thereof. The .alpha.-olefin in the ionomer resin is preferably
ethylene or propylene. Examples of the .alpha.,.beta.-unsaturated
carboxylic acid include acrylic acid, methacrylic acid, fumaric
acid, maleic acid and crotonic acid, with acrylic acid and
methacrylic acid being especially preferred. Examples of the
.alpha.,.beta.-unsaturated carboxylic acid ester include the
methyl, ethyl, propyl, n-butyl and isobutyl esters of acrylic acid,
methacrylic acid, fumaric acid and maleic acid. Acrylic acid esters
and methacrylic acid esters are especially preferred. Examples of
neutralizing metal ions include alkali metal ions, such as sodium
ions, potassium ions and lithium ions; divalent metal ions, such as
zinc ions, calcium ions and magnesium ions; trivalent metal ions,
such as aluminum ions and neodymium ions; and mixtures thereof. Of
these, from the standpoint of rebound, durability and the like,
preferred use may be made of, for example, sodium ions, zinc ions
and lithium ions. The outer layer ionomer is preferably composed of
a high acid (i.e., having an acid content of at least 16 wt %)
ionomer resin, or a high acid ionomer mixture. A mixture of two or
more high acid (i.e., having an acid content of at least 16 wt %)
ionomer resins neutralized to various degrees with different metal
ions is even more preferred.
[0122] Commonly used additives, such as pigments, fillers for
adjusting the specific gravity, dispersants, antioxidants,
ultraviolet absorbers and light stabilizers, may be suitably added
and blended in preparing the above outer layer-forming ionomer.
Combined Thickness of Outer Intermediate Layer, Inner Intermediate
Layer, Outer Envelope Layer and Inner Envelope Layer
[0123] Of the cover layers which encase the core, the combined
thickness of those cover layers exclusive of the outer layer, that
is, the combined thickness of the outer intermediate layer, inner
intermediate layer, outer envelope layer and inner envelope layer,
is preferably at least 1.0 mm, more preferably at least 1.5 mm, and
even more preferably at least 2.0 mm. The upper limit is preferably
not more than 10.0 mm, more preferably not more than 5.0 mm, and
even more preferably not more than 4.0 mm. When the above combined
thickness falls outside of the above range, the spin rate-lowering
effect on shots with a W#1 may be inadequate, as a result of which
a good distance may not be achieved.
Relationship Among Outer Layer Hardness, Intermediate Layer
Hardness, Envelope Layer Hardness, Average Core Hardness and Core
Center Hardness
[0124] In this invention, letting the average hardness of the core
be expressed by the following formula:
[0125] average core hardness (Shore D)=[core surface hardness
(Shore D)+core center hardness (Shore D)]/2, it is critical for the
outer layer hardness (Shore D) to be higher than the average core
hardness and for each of the envelope layers and the intermediate
layers to be softer than the outer layer.
[0126] The difference between the outer layer hardness and the
average core hardness, expressed in terms of the Shore hardness, is
preferably at least 5, more preferably at least 10, and even more
preferably at least 15. The upper limit is preferably not more than
40, more preferably not more than 35, and even more preferably not
more than 30. Outside of the above range, the reduction in the spin
rate on shots with a W#1 may be inadequate, as a result of which a
good distance may not be achieved, or the feel of the ball on shots
with a W#1 may become too hard.
[0127] Also, although not subject to any particular limitation, in
the present invention, it is preferable for the Shore D hardness
relationship among the envelope layers, intermediate layers and
outer layer to satisfy the following conditions:
outer layer hardness>outer intermediate layer hardness>inner
intermediate layer hardness>outer envelope layer
hardness>inner envelope layer hardness.
The Shore D hardness relationship more preferably satisfies the
following conditions:
outer layer hardness>outer intermediate layer hardness>inner
intermediate layer hardness>outer envelope layer
hardness>inner envelope layer hardness>core center
hardness.
Outside of the above hardness relationship, the spin rate on shots
with a W#1 may become too high, as a result of which a good
distance may not be achieved.
Relationship Among Outer Layer Thickness, Intermediate Layer
Thicknesses, Envelope Layer Thicknesses and Core Diameter
[0128] Although not subject to any particular limitation, it is
preferable for the outer intermediate layer, inner intermediate
layer, outer envelope layer and inner envelope layer to each have a
thickness which is similar to or less than that of the outer
layer.
[0129] In addition, the value expressed as "(outer intermediate
layer thickness+inner intermediate layer thickness)/outer layer
thickness" is preferably at least 0.75, more preferably at least
0.8, and even more preferably at least 0.9. The upper limit is
preferably not more than 1.5, more preferably not more than 1.3,
and even more preferably not more than 1.1. Outside of the above
thickness relationship, the spin rate on shots with a W#1 may
become too high, as a result of which a good distance may not be
achieved.
[0130] Also, the value expressed as "(outer envelope layer
thickness+inner envelope layer thickness)/outer layer thickness" is
preferably at least 0.75, more preferably at least 0.8, and even
more preferably at least 0.9. The upper limit is preferably not
more than 1.5, more preferably not more than 1.3, and even more
preferably not more than 1.1. Outside of the above thickness
relationship, the spin rate on shots with a W#1 may become too
high, as a result of which a good distance may not be achieved.
[0131] Moreover, the value expressed as "(outer intermediate layer
thickness+inner intermediate layer thickness)/(outer envelope layer
thickness+inner envelope layer thickness)" is preferably at least
0.75, more preferably at least 0.8, and even more preferably at
least 0.9. The upper limit is preferably not more than 1.5, more
preferably not more than 1.3, and even more preferably not more
than 1.1. Outside of the above thickness relationship, the spin
rate on shots with a W#1 may become too high, as a result of which
a good distance may not be achieved.
[0132] Also, it is preferable for the following relationship to be
satisfied:
outer layer thickness (outer intermediate layer thickness+inner
intermediate layer thickness+outer envelope layer thickness+inner
envelope layer thickness)<core diameter.
Outside of the above thickness relationship, the spin rate on shots
with a W#1 may become too high, as a result of which a good
distance may not be achieved.
[0133] In addition, the value expressed as "outer layer
thickness/(outer intermediate layer thickness+inner intermediate
layer thickness+outer envelope layer thickness+inner envelope layer
thickness)" is preferably at least 0.1, more preferably at least
0.2, and even more preferably at least 0.4. The upper limit is
preferably not more than 1, more preferably not more than 0.8, and
even more preferably not more than 0.6. Outside of the above
thickness relationship, the spin rate on shots with a W#1 may
become too high, as a result of which a good distance may not be
achieved.
[0134] Multi-piece solid golf balls having the above-described
core, envelope layers, intermediate layers and outer layer can be
manufactured by a known process such as injection molding. More
specifically, a multi-piece solid golf ball having a construction
of six or more layers can be obtained by press-molding or
injection-molding a core composed primarily of a rubber material,
successively forming envelope layers and intermediate layers around
the core using predetermined injection molds, then
injection-molding an outer layer material over the resulting
intermediate layer-encased sphere. Alternatively, use may be made
of another method of forming the outer layer, wherein a pair of
half-cups are molded beforehand using the above-described outer
layer material, the intermediate layer-encased sphere is enclosed
in these half-cups, and molding under applied pressure is carried
out at from 120 to 170.degree. C. for 1 to 5 minutes.
[0135] In the golf ball of the invention, to further improve the
aerodynamic properties and thereby increase the distance traveled
by the ball, as in conventional golf balls, it is desirable to form
a plurality of dimples on the surface of the ball. By optimizing
dimple parameters such as the types and total number of dimples,
owing to synergistic effects with the above-described ball
construction, the trajectory is more stable, making it possible to
obtain a golf ball having an excellent distance performance.
Moreover, the ball surface may be subjected to various types of
treatment, such as surface preparation, stamping and painting, in
order to enhance the design and durability of the golf ball.
[0136] First, the total number of dimples, although not subject to
any particular limitation, may be set to preferably at least 280,
more preferably at least 300, and even more preferably at least
320. The upper limit may be set to preferably not more than 360,
more preferably not more than 350, and even more preferably not
more than 340. If the number of dimples is higher than the above
range, the ball trajectory may become lower, possibly decreasing
the distance traveled by the ball. On the other hand, if the number
of dimples is lower than the above range, the ball trajectory may
become higher, as a result of which an increased distance may not
be achieved.
[0137] The shapes of the dimples are not limited to circular
shapes; one or more type from among, for example, various polygonal
shapes, dewdrop shapes and oval shapes may be suitably selected. In
cases where, for example, 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.
[0138] 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 a 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 900. Also, to optimize
the trajectory of the ball, the value V.sub.0 obtained by dividing
the spatial volume of each dimple below the flat plane
circumscribed by the edge of that dimple by the volume of a
cylinder whose base is the flat plane and whose height is the
maximum depth of the dimple from the base is preferably at least
0.35 but not more than 0.80. In addition, the value VR, which is
the sum of the volumes of the individual dimples formed below the
flat planes circumscribed by the edges of the respective dimples,
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 the above ranges in 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.
[0139] The golf ball of the invention, which can be manufactured so
as to conform with the Rules of Golf for competitive play, may be
produced to a ball diameter which is of a size that will not pass
through a ring having an inside diameter of 42.672 mm, but is not
more than 42.80 mm, and to a weight of generally from 45.0 to 45.93
g.
[0140] As shown above, by having the core composed of an elastomer,
by forming the envelope of two layers--an inner envelope layer and
an outer envelope layer, by forming the intermediate layer of two
layers--an inner intermediate layer and an outer intermediate
layer, and by optimizing the respective thicknesses and hardnesses
of the core, the envelope layers, the intermediate layers and the
outer layer as described above, the spin rate of the ball on full
shots with a driver can be lowered, enabling both a further
increase in the distance traveled by the ball and also a good feel
on impact to be achieved. The golf ball of the invention is
especially useful as a golf ball for ordinary amateur golfers
having head speeds which are not very high.
EXAMPLES
[0141] Examples of the invention and Comparative Examples are given
below by way of illustration, and not by way of limitation.
Example I and Example II
Formation of Core
[0142] Rubber compositions were formulated as shown in Table 1,
then molded and vulcanized at 155.degree. C. for 21 minutes to
produce cores.
TABLE-US-00001 TABLE 1 Parts by weight Example I Example II Core
Polybutadiene A 70 70 formulation Polybutadiene B 20 20
Polyisoprene rubber 10 10 Zinc acrylate 36.0 40.4 Peroxide 1.05
1.05 Antioxidant 0.2 0.2 Zinc oxide 32.2 30.7 Sulfur 0.085 0.085
Zinc salt of 0.4 0.4 pentachlorothiophenol Zinc stearate 5 5
Sulfur/peroxide (weight ratio) 0.08 0.08 Details on the materials
in Table 1 are given below. Polybutadiene A: Available under the
trade name "BR730" from JSR Corporation. Polybutadiene B: Available
under the trade name "BR51" from JSR Corporation. Polyisoprene
rubber: Available under the trade name "IR2200" from JSR
Corporation. Peroxide: Dicumyl peroxide, available under the trade
name "Percumyl D" from NOF Corporation. Antioxidant:
2,2'-Methylenebis(4-methyl-6-t-butyl-phenol), available under the
trade name "Nocrac NS-6" from Ouchi Shinko Chemical Industry Co.,
Ltd.
Formation of Envelope Layers, Intermediate Layers and Outer
Layer
[0143] Next, an inner envelope layer, an outer envelope layer, an
inner intermediate layer, an outer intermediate layer and an outer
layer formulated as shown in Table 2 were successively
injection-molded over the core obtained above, thereby producing a
multi-piece solid golf ball having a six-layer construction in
which five cover layers are formed over the core. At this time, the
dimples shown in FIG. 2 were formed on the surface of the outer
layer. Details on the dimples are given in Table 3.
TABLE-US-00002 TABLE 2 Formulation (pbw) No. 1 No. 2 No. 3 No. 4
No. 5 AM7317 25 AM7318 50 AM7329 25 AN4319 30 100 AN4221C 60
HPF1000 100 HPF2000 100 Dynaron 6100P 10 Polyethylene wax 1
Magnesium stearate 1.7 60 100 Magnesium oxide 1.3 2.8 Titanium
oxide 2.8 Details on the materials in Table 2 are given below.
AM7317, AM7318: High-acid-content ionomers available from
DuPont-Mitsui Polychemicals Co., Ltd. AM7329: An ionomer available
from DuPont-Mitsui Polychemicals Co., Ltd. AN4319, AN4221C:
Available under the trade name "Nucrel" from DuPont-Mitsui
Polychemicals Co., Ltd. HPF1000, HPF2000: HPF polymers available
from E.I. DuPont de Nemours & Co. Dynaron 6100P: A hydrogenated
polymer available from JSR Corporation. Polyethylene wax: A
low-molecular-weight polyethylene wax available under the trade
name "Sanwax 161P" from Sanyo Chemical Industries, Ltd. Magnesium
oxide: Available under the trade name "Kyowamag MF150" from Kyowa
Chemical Industry Co., Ltd.
TABLE-US-00003 TABLE 3 Number of Diameter Depth No. dimples (mm)
(mm) V.sub.0 SR VR 1 12 4.6 0.15 0 .47 81 0.78 2 234 4.4 0.15 0 .47
3 60 3.8 0.14 0 .47 4 6 3.5 0.13 0 .46 5 6 3.4 0.13 0 .46 6 12 2.6
0.10 0 .46 Total 330 Dimple Definitions Diameter: Diameter of flat
plane circumscribed by edge of dimple. Depth: Maximum depth of
dimple from flat plane circumscribed by edge of dimple. V.sub.0:
Spatial volume of dimple below flat plane circumscribed by dimple
edge, divided by volume of cylinder whose base is the flat plane
and whose height is the maximum depth of dimple from the base. SR:
Sum of individual dimple surface areas, each defined by the flat
plane circumscribed by the edge of the dimple, as a percentage of
surface area of ball sphere were it to have no dimples thereon
(units: %). VR: Sum of volumes of individual dimples formed below
flat planes circumscribed by the edges of the respective dimples,
as a percentage of volume of ball sphere were it to have no dimples
thereon (units: %).
[0144] The various golf balls obtained were tested and evaluated by
the methods described below with regard to properties of the
various layers, such as thickness, hardness and deflection, and
also flight performance and feel. The results are shown in Tables 4
and 5. All measurements were carried out in a 23.degree. C.
atmosphere.
(1) Core Deflection (mm)
[0145] The core was placed on a hard plate, and the amount of
deformation by the core when compressed under a final load of 1,275
N (130 kgf) from an initial load state of 98 N (10 kgf) was
measured.
(2) Core Surface Hardness
[0146] The average of the values obtained by setting a durometer
indenter substantially perpendicular to the spherical surface of
the core and measuring the JIS-C hardness (in accordance with
JIS-K6301) at two randomly selected points on the core surface. In
addition, the Shore D hardness of the core surface was measured by
the same method as just described, but using a type D durometer in
accordance with ASTM-2240. This hardness was designated as the core
surface hardness H.
(3) Core Cross-Sectional Hardnesses
[0147] The core was cut into half, creating a flat plane. The
durometer indenter was set substantially perpendicular thereto at
the place of measurement and the JIS-C hardness was measured (in
accordance with JIS-K6301).
[0148] Cross-sectional hardnesses were measured at the following
places.
[0149] C0: Center of core
[0150] C2: A position 2 mm from center of core
[0151] C4: A position 4 mm from center of core
[0152] C6: A position 6 mm from center of core
[0153] C8: A position 8 mm from center of core
[0154] C10: A position 10 mm from center of core
[0155] C12: A position 12 mm from center of core
[0156] C14: A position 14 mm from center of core
[0157] C16: A position 16 mm from center of core
[0158] In addition, the Shore D hardness at the center of the core
was measured. The Shore D hardness was measured by the same method
as described above, but using a type D durometer in accordance with
ASTM-2240.
(4) Average Core Hardness
[0159] Average core hardness=(core surface hardness+core center
hardness)/2
(5) Material Hardnesses of Envelope Layers, Intermediate Layers and
Outer Layer (hardnesses of molded sheets)
[0160] The materials used to form the respective layers were molded
into sheets having a thickness of about 2 mm and held for two weeks
at 23.degree. C., following which they were stacked to a thickness
of at least 6 mm and the Shore D hardnesses were measured with a
type D durometer in accordance with AASTM D-2240.
(6) Flight Performance on Shots with a Driver
[0161] The distance traveled by the ball when hit at a head speed
(HS) of 40 m/s with a driver (abbreviated below as "W#1"; TourStage
GR (2010 model), manufactured by Bridgestone Sports Co., Ltd.; loft
angle, 10.5.degree.) mounted on a golf swing robot was measured.
The results were rated according to the criteria shown below. The
spin rate was the value measured for the ball, using an apparatus
for measuring initial conditions, immediately after the ball was
hit in the same way as described above.
[0162] Good: Total distance was 204 m or more
[0163] NG: Total distance was less than 204 m
(7) Feel
[0164] Amateur golfers who value distance and have head speeds (HS)
of 35 to 45 m/s carried out sensory tests on the ball when struck
with a driver (W#1). The results were rated as follows.
[0165] Good: The ball had a good, soft feel
[0166] NG: The ball had a hard feel
TABLE-US-00004 TABLE 4 Example I Example II Core Diameter (mm) 35.5
35.5 Weight (g) 29.0 29.0 Deflection (mm) 3.7 3.4 Surface hardness
(Shore D) 55 59 Center hardness (Shore D) 38 38 Average core
hardness Shore D 46 49 JIS-C 72 75 Surface hardness H- Shore D 17
21 Center hardness C0 Core hardness profile CO (center) 60 61
(JIS-C) C2 (2 mm from center) 61 61 C4 (4 mm from center) 62 61 C6
(6 mm from center) 63 62 C8 (8 mm from center) 64 64 C10 (10 mm
from center) 65 65 C12 (12 mm from center) 68 69 C14 (14 mm from
center) 76 79 C16 (16 mm from center) 79 84 H (surface) 83 88
Surface hardness H- JIS-C 23 27 Center hardness C0 Cross-sectional
hardness C4- JIS-C 2 0 Center hardness C0 Cross-sectional hardness
C10- JIS-C 3 4 Center hardness C4 Surface hardness H- JIS-C 18 23
Cross-sectional hardness C10 Inner envelope layer Material (type)
No. 5 No. 5 Thickness (mm) 0.6 0.6 Specific gravity (g/cm.sup.3)
0.96 0.96 Sheet (Shore D) 46 46 Inner envelope layer- Diameter (mm)
36.7 36.7 encased sphere Weight (g) 31.4 31.4 Outer envelope layer
Material (type) No. 4 No. 4 Thickness (mm) 0.6 0.6 Specific gravity
(g/cm.sup.3) 0.95 0.95 Sheet (Shore D) 48 48 Outer envelope layer-
Diameter (mm) 37.9 37.9 encased sphere Weight (g) 33.8 33.8 Inner
intermediate Material (type) No. 3 No. 3 layer Thickness (mm) 0.6
0.6 Specific gravity (g/cm.sup.3) 0.96 0.96 Sheet (Shore D) 51 51
Inner intermediate Diameter (mm) 39.1 39.1 layer-encased sphere
Weight (g) 36.5 36.5 Outer intermediate Material (type) No. 2 No. 2
layer Thickness (mm) 0.6 0.6 Specific gravity (g/cm.sup.3) 0.95
0.95 Sheet (Shore D) 55 55 Outer intermediate Diameter (mm) 40.3
40.3 layer-encased sphere Weight (g) 39.4 39.4 Outer layer Material
(type) No. 1 No. 1 Thickness (mm) 1.2 1.2 Specific gravity
(g/cm.sup.3) 0.97 0.97 Sheet (Shore D) 65 65 Ball Diameter (mm)
42.7 42.7 Weight (g) 45.5 45.5 Outer layer hardness - Outer
intermediate 10 10 layer hardness (Shore D) Outer layer hardness -
Average 19 16 core hardness (Shore D)
TABLE-US-00005 TABLE 5 Example I Example II Flight (W#1, HS 40 m/s)
Spin rate (rpm) 3,127 3,169 Total distance(m) 204.7 204.3 Rating
good good Feel Rating good good
* * * * *