Patent Application
20250041669
The present disclosure relates to a golf ball, and relates to a golf ball that easily stops on approach shots.
A golf ball is generally composed of a spherical core and a cover. The spherical core is formed from a rubber composition containing a base rubber and a co-crosslinking agent, and has a hardness distribution.
JP 2014-050696 A discloses a golf ball comprising a core and a cover, wherein the core is formed from a rubber composition containing a base rubber, a co-crosslinking agent, a crosslinking initiator and a metal oxide, the co-crosslinking agent is methacrylic acid, the metal oxide is zinc oxide, the rubber composition contains an organic sulfur compound and contains the crosslinking initiator in an amount from 1.2 parts by mass to 5 parts by mass with respect to 100 parts by mass of the base rubber, and the ball product has an initial velocity of 74.3 m/s or more.
JP 2014-069045 A discloses a solid golf ball comprising a core and a cover, the core being formed from a rubber composition containing a base rubber, a co-crosslinking agent, a crosslinking initiator and a metal oxide, wherein a mixture of a polybutadiene and a styrene-butadiene rubber is used as the base rubber, an amount of a styrene bond in the styrene-butadiene rubber is 35 mass % or less, methacrylic acid is used as the co-crosslinking agent, the core has a deflection (CH) ranging from 2.5 mm to 7.0 mm when applying a load from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) to the core, and a ratio (VR) of a total spatial volume of dimples that are formed below a plane circumscribed by an edge of the dimples to a volume of a virtual sphere that is assumed to have no dimples on the ball surface ranges from 0.95 to 1.7.
JP 2012-228470 A discloses a practice golf ball comprising a core and a cover, the core being formed from a rubber composition containing a base rubber, a co-crosslinking agent, a crosslinking initiator and a metal oxide, wherein a mixture of a polybutadiene and a styrene-butadiene rubber and/or an isoprene rubber is used as the base rubber, methacrylic acid is used as the co-crosslinking agent, the core has a deflection CH ranging from 2.5 mm to 7.0 mm when applying a load from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) to the core, the ball has an initial velocity of 70 m/s or less, and a ratio (VR) of a total spatial volume of dimples that are formed below a plane circumscribed by an edge of the dimples to a volume of a virtual sphere that is assumed to have no dimples on the ball surface ranges from 0.95 to 1.7.
JP 2012-228468 A discloses a practice golf ball comprising a core and a cover, the core being formed from a rubber composition containing a base rubber, a co-crosslinking agent, a crosslinking initiator and a metal oxide, wherein methacrylic acid is used as the co-crosslinking agent, zinc oxide is used as the metal oxide, when a JIS-C hardness at a core surface is (A), a JIS-C hardness at a position 2 mm inside the core surface is (B), a JIS-C hardness at a position 5 mm inside the core surface is (C), a JIS-C hardness at a position 10 mm inside the core surface is (D), a JIS-C hardness at a position 15 mm inside the core surface is (E), and a JIS-C hardness at a core center is (F) in a hardness distribution of the core, (A) ranges from 65 to 77, (B) ranges from 59 to 70, (C) ranges from 61 to 74, (D) ranges from 59 to 75, (E) ranges from 61 to 70, (F) ranges from 57 to 67, a hardness relationship of (A)>(B)<(C)>(D)>(E)>(F) is satisfied, a value of (A)-(F) is 19 or less, (A) is the highest one among (A) to (F), a value of (A)-(C) ranges from 0 to 8, the core has a specific gravity ranging from 1.05 to 1.2, a resin component of the cover is composed primarily of a polyurethane, the cover has a thickness ranging from 0.3 mm to 1.9 mm, the cover has a material hardness ranging from 30 to 48 in Shore D hardness, when deflections of the core and the ball when applying a load from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) to the core and the ball, are each represented by (CH) and (BH1), (CH) ranges from 2.8 mm to 7.0 mm, a value of (CH)/(BH1) ranges from 0.95 to 1.1, and a ratio (VR) of a total spatial volume of dimples that are formed below a plane circumscribed by an edge of the dimples to a volume of a virtual sphere that is assumed to have no dimples on the ball surface ranges from 0.95 to 1.7.
JP 2012-228465 A discloses a practice golf ball comprising a core and a cover, the core being formed from a rubber composition containing a base rubber, a co-crosslinking agent, a crosslinking initiator and a metal oxide, wherein methacrylic acid is used as the co-crosslinking agent, when a JIS-C hardness at a core surface is (A), a JIS-C hardness at a position 2 mm inside the core surface is (B), a JIS-C hardness at a position 5 mm inside the core surface is (C), a JIS-C hardness at a position 10 mm inside the core surface is (D), a JIS-C hardness at a position 15 mm inside the core surface is (E), and a JIS-C hardness at a core center is (F) in a hardness distribution of the core, (A) ranges from 70 to 88, (B) ranges from 64 to 83, (C) ranges from 66 to 85, (D) ranges from 64 to 80, (E) ranges from 61 to 75, (F) ranges from 58 to 72, a hardness relationship of (A)>(B)<(C)>(D)>(E)>(F) is satisfied, a value of (A)-(F) is 19 or less, (A) is the highest one among (A) to (F), a value of (A)-(C) ranges from 1 to 8, the core has a specific gravity ranging from 1.05 to 1.2, a resin component of the cover is composed primarily of a polyurethane, the cover has a thickness ranging from 0.3 mm to 1.9 mm, the cover has a material hardness ranging from 30 to 57 in Shore D hardness, when deflections of the core and the ball when applying a load from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) to the core and the ball, are each represented by (CH) and (BH1), (CH) ranges from 2.0 mm to 4.0 mm, and a value of (CH)/(BH1) ranges from 0.95 to 1.1.
JP 2012-228461 A discloses a practice golf ball comprising a core, a cover and a clear paint layer, the core being formed from a rubber composition containing a base rubber, a co-crosslinking agent, a crosslinking initiator and a metal oxide, wherein methacrylic acid is used as the co-crosslinking agent, a resin material forming the cover has a strength at break ranging from 20 MPa to 80 MPa and an elongation ranging from 150% to 600%, and the ball has an initial velocity (BV) of 76 m/s or less.
JP 2012-228458 A discloses a practice golf ball comprising a core and a cover, the core being formed from a rubber composition containing a base rubber, a co-crosslinking agent, a crosslinking initiator and a metal oxide, wherein methacrylic acid is used as the co-crosslinking agent, and when deflections of the core and the ball when applying a load from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) to the core and the ball, are each represented by (CH) and (BH1), a value of (CH)/(BH1) ranges from 0.95 to 1.1.
JP 2012-228457 A discloses a practice golf ball comprising a core and a cover, wherein the ball has a deflection BH ranging from 2.0 mm to 4.5 mm when applying a load from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) to the ball, and a carry C of the ball obtained by installing TourStage X-DRIVE701 (loft angle: 9°) available from Bridgestone Sports Co., Ltd. as a driver (W#1) on a hitting robot and hitting the ball at a head speed (HS) of 52 m/s, is preset to adjust the deflection BH of the ball such that the following formula (1): C=A−33×BH (1) (in the formula, 295≤A≤325) is satisfied.
JP 2012-228456 A discloses a practice golf ball comprising a core and a cover, wherein when a deflection of the ball when applying a load from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) to the ball is represented by BH1 (mm) and an initial velocity of the ball is represented by BV1 (m/s) upon initial measurement, and a deflection of the ball when applying a load from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) to the ball is represented by BH2 (mm) and an initial velocity of the ball is represented by BV2 (m/s) upon another measurement after the ball has been left to stand for 350 days from the initial measurement, a difference of BH2-BH1 is 0.2 mm or less and a difference of BV2-BV1 is 0.3 m/s or less.
JP 2012-228452 A discloses a practice golf ball comprising a core and a cover, the core being formed from a rubber composition containing a base rubber, a co-crosslinking agent, a crosslinking initiator and a metal oxide, wherein methacrylic acid is used as the co-crosslinking agent, and a resin material forming the cover has a strength at break ranging from 20 MPa to 80 MPa and an elongation ranging from 150% to 600%.
JP 2012-228448 A discloses a practice golf ball comprising a core and a cover, the core being formed from a rubber composition containing a base rubber and a co-crosslinking agent, wherein methacrylic acid is used as the co-crosslinking agent, and the ball has an initial velocity of 76 m/s or less.
JP 2012-228447 A discloses a practice golf ball comprising a core and a cover, wherein the cover has a material hardness ranging from 30 to 57 in Shore D hardness, and when an initial velocity of the core is represented by CV (m/s) and an initial velocity of the ball is represented by BV1 (m/s), a value of CV-BV1 satisfies the following formula (1): (CV−BV1)=0.7×(cover thickness)-b (1) (in the formula, 0.1≤b≤1.0).
JP S60-92780 A discloses a range golf ball, obtained by vulcanizing a composition containing 100 parts by weight of a base rubber, 3 to 35 parts by weight of a low-resilient rubber, 20 to 30 parts by weight of methacrylic acid, and 20 to 50 parts by weight of a metal compound that can form a metal salt with methacrylic acid.
JP H10-192446 A discloses a solid golf ball comprising a core and a cover formed on the core, wherein the core is obtained from a rubber composition obtained by blending 20 to 40 parts by weight of methacrylic acid and 20 to 40 parts by weight of zinc oxide to 100 parts by weight of a base rubber, generating a basic zinc methacrylate as a main component in the rubber, and conducting a reaction of 0.1 to 3.0 parts by weight of an organic peroxide and 0.1 to 3.0 parts by weight of an organic sulfur compound with the composition.
JP 2021-62036 A discloses a multi-piece solid golf ball comprising a core, an intermediate layer and a cover, wherein the core is primarily formed from a base rubber and has a diameter of 32 mm or more, the intermediate layer and the cover are each formed from a resin material, and when a Shore C hardness at a core center is Cc, a Shore C hardness at a position 2 mm from the core center is C2, a Shore C hardness at a position 4 mm from the core center is C4, a Shore C hardness at a position 6 mm from the core center is C6, a Shore C hardness at a position 8 mm from the core center is C8, a Shore C hardness at a position 10 mm from the core center is C10, a Shore C hardness at a position 12 mm from the core center is C12, a Shore C hardness at a position 14 mm from the core center is C14, a Shore C hardness at a position 16 mm from the core center is C16, a Shore C hardness at a core surface is Cs, a Shore C hardness at a position 3 mm inside the core surface is Cs-3, and a hardness at a midpoint between the core surface and the core center is Cm in an internal hardness of the core, a value of C8-C6, a value of C6-C4, a value of C4-C2 and a value of C2-Cc are each 4.0 or less, a value of C16-C14, a value of C14-C12, a value of C12-C10 and a value of C10-C8 are each 5.5 or less, the following formulae (1), (2) and (3) are satisfied:
Cs−Cc≥22 (1)
(Cs−Cm)/(C4−Cc)≥4.0 (2)
Cs−Cs−3≤5.0 (3)
and a surface hardness of a spherical body (intermediate layer-covering spherical body) having the core covered with the intermediate layer and a surface hardness of the ball satisfy the following formula:
JP 2016-112308 A discloses a multi-piece solid golf ball comprising a core, a cover and an intermediate layer therebetween, wherein a surface hardness of the core, a surface hardness of a spherical body (intermediate layer-covering spherical body) having the core covered with the intermediate layer and a surface hardness of the ball, expressed in terms of Shore D hardness, satisfy the following relationship: surface hardness of ball s surface hardness of intermediate layer-covering spherical body≥surface hardness of core, a thickness of the intermediate layer and a thickness of the cover satisfy the following relationship: (thickness of intermediate layer-thickness of cover)≥0, and a hardness distribution of the core, expressed in terms of JIS-C hardness, satisfies the following relationships: 22≤surface hardness of core (Cs)—center hardness of core (Cc), 5≥[hardness (C5) at a position 5 mm from core center—center hardness of core (Cc)]>0, and [surface hardness of core (Cs)—center hardness of core (Cc)]/[hardness at midpoint between surface and center of core (Cm)—center hardness of core (Cc)]≥4.
An approach shot is a shot that brings a golf ball close to the cup from around the green, and controllability of a golf ball on approach shots is important for making a golf score.
A high-skilled golfer also has a small variation in the hitting point on approach shots, so the spin rate is stable. However, a ball with a fast initial velocity on approach shots is easy to roll and is hard to be controlled. In addition, for an average golfer, because of the large variation in the hitting point, the spin rate is unstable, and it is difficult to stop the golf ball on approach shots. In particular, if the ball is hit fast on approach shots, the ball rolls over the green surface, and stops greatly away from the target point.
The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a golf ball that has a low initial velocity on approach shots, excellent controllability, and a good shot feeling on approach shots by improving the core.
The present disclosure that has solved the above problem provides a golf ball comprising a spherical core, at least one intermediate layer positioned outside the spherical core, and a cover positioned outside the intermediate layer, wherein
If the spherical core of the golf ball according to the present disclosure is constituted as above, the ball initial velocity on approach shots can be lowered. The golf ball having the low initial velocity on approach shots does not roll too much and thus has excellent controllability. In addition, the above spherical core provides the golf ball with a good shot feeling on approach shots.
According to the present disclosure, a golf ball that has a low initial velocity on approach shots, excellent controllability, and a good shot feeling on approach shots is provided.
The figure is a partially cutaway cross-sectional view showing a golf ball according to one embodiment of the present disclosure.
The present disclosure provides a golf ball comprising a spherical core, at least one intermediate layer positioned outside the spherical core, and a cover positioned outside the intermediate layer, wherein
The center hardness (Shore C hardness) of the spherical core, and the hardness (Shore C hardness) at each point of 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12.5 mm and 15 mm from the center of the spherical core toward the surface of the spherical core are obtained by cutting the spherical core into two hemispheres along a plane passing through the center of the spherical core to obtain a cut plane, and measuring the hardness at the central point of the cut plane and the hardness at the point having the predetermined distance from the central point. The surface hardness of the spherical core is the hardness measured on the surface of the spherical core.
In a preferable embodiment of the present disclosure, each of (H2.5−H0), (H5—H2.5), (H7.5−H5), (H10-H7.5), (H12.5−H10), (H15−H12.5), and (HS-H15) is preferably 5 or less. If each of (H2.5−H0), (H5−H2.5), (H7.5−H5), (H10-H7.5), (H12.5−H10), (H15−H12.5), and (HS-H15) is 5 or less, the core can smoothly deform as a whole, and thus the shot feeling on various numbered-iron shots is better.
Each of (H2.5−H0), (H5−H2.5), (H7.5−H5), (H10-H7.5), (H12.5−H10), (H15−H12.5), and (HS-H15) is preferably 0 or more. If each of (H2.5−H0), (H5−H2.5), (H7.5−H5), (H10-H7.5), (H12.5−H10), (H15−H12.5), and (HS-H15) is 0 or more, the core has an outer-hard and inner-soft structure, and the flight distance performance on driver shots is better.
The hardness difference (H2.5−H0) between the hardness (H2.5) at 2.5 mm point from the center of the spherical core and the center hardness (H0) of the spherical core is preferably 5 or less, more preferably 4.5 or less, and even more preferably 4 or less in Shore C hardness. In addition, the lower limit of the hardness difference (H2.5−H0) is not particularly limited, and the hardness difference (H2.5−H0) is preferably 0 or more, more preferably 1 or more, and even more preferably 1.5 or more in Shore C hardness. If the hardness difference (H2.5−H0) falls within the above range, the spin rate on driver shots is lowered.
The hardness difference (H7.5−H5) between the hardness (H7.5) at 7.5 mm point from the center of the spherical core and the hardness (H5) at 5 mm point from the center of the spherical core is preferably 5 or less, more preferably 4.8 or less, and even more preferably 4.5 or less, and is preferably 0 or more, more preferably 1 or more, and even more preferably 2 or more in Shore C hardness. If the hardness difference (H7.5−H5) falls within the above range, the shot feeling on driver shots is better.
The hardness difference between the hardness (H10) at 10 mm point from the center of the spherical core and the hardness (H7.5) at 7.5 mm point from the center of the spherical core (H10−H7.5) is preferably 5 or less, more preferably 4.8 or less, and even more preferably 4.5 or less, and is preferably 0 or more, more preferably 1 or more, and even more preferably 2 or more in Shore C hardness. If the hardness difference (H10−H7.5) falls within the above range, the shot feeling on iron shots is better.
The hardness difference (H15−H12.5) between the hardness (H15) at 15 mm point from the center of the spherical core and the hardness (H12.5) at 12.5 mm point from the center of the spherical core is preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less, and is preferably 0 or more, more preferably 0.3 or more, and even more preferably 0.5 or more in Shore C hardness. If the hardness difference (H15−H12.5) falls within the above range, the shot feeling on iron shots is better.
The hardness difference (HS−H15) between the surface hardness (HS) of the spherical core and the hardness (H15) at 15 mm point from the center of the spherical core is preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less, and is preferably 0 or more, more preferably 0.3 or more, and even more preferably 0.5 or more in Shore C hardness. If the hardness difference (HS−H15) falls within the above range, a better shot feeling is obtained when hitting a golf ball with a putter.
The hardness difference (HS−H0) between the surface hardness (HS) and the center hardness (H0) of the spherical core is preferably 20 or less, more preferably 19 or less, and even more preferably 18 or less, and is preferably 5 or more, more preferably 6 or more, and even more preferably 7 or more in Shore C hardness. If the hardness difference (HS−H0) falls within the above range, the spin performance is better and the shot feeling is better on a short iron shot.
The surface hardness (HS) of the spherical core is not particularly limited, and the surface hardness (HS) of the spherical core is preferably 70 or more, more preferably 71 or more, and even more preferably 72 or more, and is preferably 80 or less, more preferably 79 or less, and even more preferably 78 or less in Shore C hardness. If the surface hardness (HS) falls within the above range, a better shot feeling is obtained when hitting a golf ball with a putter.
The center hardness (H0) of the spherical core is not particularly limited, and the center hardness (H0) of the spherical core is preferably 48 or more, more preferably 49 or more, and even more preferably 50 or more, and is preferably 60 or less, more preferably 59 or less, and even more preferably 58 or less in Shore C hardness. If the center hardness (H0) of the spherical core falls within the above range, a better shot feeling is obtained on a long shot.
The spherical core of the golf ball according to the present disclosure is preferably formed from a rubber composition (hereinafter sometimes referred to as “core rubber composition”) containing (a) a rubber component, (b) a co-crosslinking agent, and (c) a crosslinking initiator.
As (a) the rubber component, a natural rubber and/or a synthetic rubber can be used. For example, a polybutadiene rubber, a natural rubber, a butyl rubber, a polyisoprene rubber, a styrene polybutadiene rubber, or an ethylene-propylene-diene rubber (EPDM) can be used. These rubbers may be used solely, or at least two of these rubbers may be used in combination. Among them, particularly preferred is a high-cis polybutadiene having a cis-1,4 bond in an amount of 40 mass % or more, preferably 80 mass % or more, and more preferably 90 mass % or more in view of its superior processability.
The high-cis polybutadiene preferably has a 1,2-vinyl bond in an amount of 2 mass % or less, more preferably 1.7 mass % or less, and even more preferably 1.5 mass % or less. If the amount of the 1,2-vinyl bond is 2 mass % or less, the processability is better to obtain a more homogeneous rubber composition.
The high-cis polybutadiene is preferably one synthesized using a rare-earth element catalyst. When a neodymium catalyst employing a neodymium compound which is a lanthanum series rare-earth element compound, is used, a polybutadiene rubber having a high amount of the cis-1,4 bond and a low amount of the 1,2-vinyl bond is obtained with an excellent polymerization activity, and thus such polybutadiene rubber is particularly preferable.
The Mooney viscosity (ML1+4 (100° C.)) of the high-cis polybutadiene is preferably 30 or more, more preferably 32 or more, and even more preferably 35 or more, and is preferably 140 or less, more preferably 120 or less, even more preferably 100 or less, and most preferably 80 or less. It is noted that the Mooney viscosity (ML1+4 (100° C.)) in the present disclosure is a value measured according to JIS K6300 using an L rotor under the conditions of preheating time: 1 minute, rotor rotation time: 4 minutes, and temperature: 100° C.
The molecular weight distribution Mw/Mn (Mw: weight average molecular weight, Mn: number average molecular weight) of the high-cis polybutadiene is preferably 2.0 or more, more preferably 2.2 or more, even more preferably 2.4 or more, and most preferably 2.6 or more, and is preferably 6.0 or less, more preferably 5.0 or less, even more preferably 4.0 or less, and most preferably 3.4 or less. If the molecular weight distribution (Mw/Mn) of the high-cis polybutadiene is 2.0 or more, the workability is better, and if the molecular weight distribution (Mw/Mn) of the high-cis polybutadiene is 6.0 or less, the processability is higher. It is noted that the molecular weight distribution is measured by gel permeation chromatography (“HLC-8120GPC” available from Tosoh Corporation) using a differential refractometer as a detector under the conditions of column: GMHHXL (available from Tosoh Corporation), column temperature: 40° C., and mobile phase: tetrahydrofuran, and calculated by converting based on polystyrene standard.
The core rubber composition preferably contains a polybutadiene rubber and (a butyl rubber and/or a polyisoprene rubber) as the rubber component. In other words, examples of the rubber component of the core rubber composition include an embodiment that contains the polybutadiene rubber and the butyl rubber, an embodiment that contains the polybutadiene rubber and the polyisoprene rubber, and an embodiment that contains the polybutadiene rubber, the butyl rubber and the polyisoprene rubber. If the rubber component contains the butyl rubber and/or the polyisoprene rubber in addition to the polybutadiene rubber, the resilience performance of the golf ball is easily adjusted such that the desirable resilience performance can be achieved.
The ratio [polybutadiene rubber/(butyl rubber and/or polyisoprene rubber)] of the polybutadiene rubber to the (butyl rubber and/or polyisoprene rubber) is preferably 30/70 or more, more preferably 40/60 or more, and even more preferably 50/50 or more, and is preferably 95/5 or less, more preferably 90/10 or less, and even more preferably 85/15 or less in a mass ratio. If the ratio of the polybutadiene rubber to the (butyl rubber and/or polyisoprene rubber) falls within the above range, the uniformity of the rubber can be ensured, and thus the quality is stable.
The core rubber composition used in the present disclosure contains (b) a co-crosslinking agent. (b) The co-crosslinking agent has an action of crosslinking a rubber molecule by graft polymerization to the rubber component. The core rubber composition used in the present disclosure contains methacrylic acid and/or a metal salt thereof as (b) the co-crosslinking agent. If methacrylic acid and/or the metal salt thereof is contained as (b) the co-crosslinking agent, a gradual hardness gradient is easily produced, and thus the controllability on approach shots is better.
Examples of the metal ion constituting the metal salt of methacrylic acid include a monovalent metal ion such as sodium, potassium and lithium; a divalent metal ion such as magnesium, calcium, zinc, barium and cadmium; a trivalent metal ion such as aluminum; and other metal ions such as tin and zirconium. The above metal component may be used solely or as a mixture of at least two of them.
In the present disclosure, methacrylic acid is preferably used as (b) the co-crosslinking agent.
The amount of (b) the co-crosslinking agent is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, with respect to 100 parts by mass of (a) the rubber component. If the amount of (b) the co-crosslinking agent is 10 parts by mass or more, the formed core has a suitable hardness, and the durability of the golf ball is better. On the other hand, if the amount of (b) the co-crosslinking agent is 50 parts by mass or less, the formed core is not excessively hard.
(b) The co-crosslinking agent may contain an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms (excluding methacrylic acid) and/or a metal salt thereof, in addition to methacrylic acid and/or the metal salt thereof.
Examples of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms (excluding methacrylic acid) include acrylic acid, fumaric acid, maleic acid and crotonic acid.
Examples of the metal ion constituting the metal salt of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms (excluding methacrylic acid) include a monovalent metal ion such as sodium, potassium and lithium; a divalent metal ion such as magnesium, calcium, zinc, barium and cadmium; a trivalent metal ion such as aluminum; and other metal ions such as tin and zirconium. The above metal component may be used solely or as a mixture of at least two of them. Among them, the divalent metal ion such as magnesium, calcium, zinc, barium and cadmium is preferably used as the metal component. This is because if the divalent metal salt of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms is used, a metal crosslinking easily generates between the rubber molecules.
In the case that (b) the co-crosslinking agent contains the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms (excluding methacrylic acid) and/or the metal salt thereof in addition to methacrylic acid and/or the metal salt thereof, the amount of methacrylic acid and/or the metal salt thereof in (b) the co-crosslinking agent component is preferably 50 mass % or more, more preferably 60 mass % or more, and even more preferably 70 mass % or more, and is preferably 99 mass % or less, more preferably 98 mass % or less, and even more preferably 97 mass % or less. If the amount of methacrylic acid and/or the metal salt thereof falls within the above range, the reactivity in the rubber is uniform and the quality is stable. The co-crosslinking agent preferably consists of methacrylic acid and/or the metal salt thereof, and more preferably consists of methacrylic acid.
(c) The crosslinking initiator is blended to crosslink (a) the rubber component. As (c) the crosslinking initiator, an organic peroxide is suitable. Specific examples of the organic peroxide include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy) hexane and di-t-butyl peroxide. These organic peroxides may be used solely or as a mixture of at least two of them. Among them, dicumyl peroxide is preferably used.
The amount of (c) the crosslinking initiator is preferably 0.2 part by mass or more, more preferably 0.4 part by mass or more, and even more preferably 0.6 part by mass or more, and is preferably 5.0 parts by mass or less, more preferably 2.5 parts by mass or less, and even more preferably 1.0 part by mass or less, with respect to 100 parts by mass of (a) the rubber component. If the amount of (c) the crosslinking initiator falls within the above range, the formed core has a more suitable hardness and thus the golf ball has better durability.
The rubber composition preferably further contains (d) a metal compound. (d) The metal compound can be used, for example, to neutralize (b) the co-crosslinking agent in the rubber composition, or to adjust the weight of the rubber composition.
Examples of (d) the metal compound include a metal hydroxide such as magnesium hydroxide, zinc hydroxide, calcium hydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide, and copper hydroxide; a metal oxide such as magnesium oxide, calcium oxide, zinc oxide, and copper oxide; and a metal carbonate such as magnesium carbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithium carbonate, and potassium carbonate. As (d) the metal compound, the divalent metal compound is preferable, the zinc compound is more preferable. This is because the divalent metal compound reacts with the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms to form a metal crosslinking. In addition, use of the zinc compound provides a golf ball with better durability. (d) The metal compound may be used solely, or at least two of them may be used in combination.
The rubber composition preferably may further contain (e) an organic sulfur compound. (e) The organic sulfur compound is not particularly limited, as long as it is an organic compound having a sulfur atom in the molecule thereof. Examples of (e) the organic sulfur compound include an organic compound having a thiol group (—SH) or a polysulfide bond having 2 to 4 sulfur atoms (—S—S—, —S—S—S—, or —S—S—S—S—), and a metal salt thereof (-SM, —S-M-S— or the like; M is a metal atom). Examples of (e) the organic sulfur compound include compounds belonging to thiophenols, thionaphthols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, and thiazoles.
Examples of the thiophenols include thiophenol; thiophenols substituted with a fluoro group, such as 4-fluorothiophenol, 2,4-difluorothiophenol, 2,5-difluorothiophenol, 2,6-difluorothiophenol, 2,4,5-trifluorothiophenol, 2,4,5,6-tetrafluorothiophenol, and pentafluorothiophenol; thiophenols substituted with a chloro group, such as 2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol, 2,6-dichlorothiophenol, 2,4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol, and pentachlorothiophenol; thiophenols substituted with a bromo group, such as 4-bromothiophenol, 2,4-dibromothiophenol, 2,5-dibromothiophenol, 2,6-dibromothiophenol, 2,4,5-tribromothiophenol, 2,4,5,6-tetrabromothiophenol, and pentabromothiophenol; thiophenols substituted with an iodo group, such as 4-iodothiophenol, 2,4-diiodothiophenol, 2,5-diiodothiophenol, 2,6-diiodothiophenol, 2,4,5-triiodothiophenol, 2,4,5,6-tetraiodothiophenol, and pentaiodothiophenol; and their metal salts.
Examples of the thionaphthols (naphthalenethiols) include 2-thionaphthol, 1-thionaphthol, 1-chloro-2-thionaphthol, 2-chloro-1-thionaphthol, 1-bromo-2-thionaphthol, 2-bromo-1-thionaphthol, 1-fluoro-2-thionaphthol, 2-fluoro-1-thionaphthol, 1-cyano-2-thionaphthol, 2-cyano-1-thionaphthol, 1-acetyl-2-thionaphthol, 2-acetyl-1-thionaphthol, and their metal salts.
The polysulfides are organic sulfur compounds having a polysulfide bond, and examples thereof include disulfides, trisulfides, and tetrasulfides. As the polysulfides, diphenyl polysulfides are preferable.
Examples of the diphenyl polysulfides include diphenyl disulfide; diphenyl disulfides substituted with a halogen group, such as bis(4-fluorophenyl) disulfide, bis(2,5-difluorophenyl) disulfide, bis(2,6-difluorophenyl) disulfide, bis(2,4,5-trifluorophenyl) disulfide, bis(2,4,5,6-tetrafluorophenyl) disulfide, bis(pentafluorophenyl) disulfide, bis(4-chlorophenyl) disulfide, bis(2,5-dichlorophenyl) disulfide, bis(2,6-dichlorophenyl) disulfide, bis(2,4,5-trichlorophenyl) disulfide, bis(2,4,5,6-tetrachlorophenyl) disulfide, bis(pentachlorophenyl) disulfide, bis(4-bromophenyl) disulfide, bis(2,5-dibromophenyl) disulfide, bis(2,6-dibromophenyl) disulfide, bis(2,4,5-tribromophenyl) disulfide, bis(2,4,5,6-tetrabromophenyl) disulfide, bis(pentabromophenyl) disulfide, bis(4-iodophenyl) disulfide, bis(2,5-diiodophenyl) disulfide, bis(2,6-diiodophenyl) disulfide, bis(2,4,5-triiodophenyl) disulfide, bis(2,4,5,6-tetraiodophenyl) disulfide, and bis(pentaiodophenyl) disulfide; and diphenyl disulfides substituted with an alkyl group, such as bis(4-methylphenyl) disulfide, bis(2,4,5-trimethylphenyl) disulfide, bis(pentamethylphenyl) disulfide, bis(4-t-butylphenyl) disulfide, bis(2,4,5-tri-t-butylphenyl) disulfide, and bis(penta-t-butylphenyl) disulfide.
Examples of the thiurams include thiuram monosulfides such as tetramethylthiuram monosulfide; thiuram disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetrabutylthiuram disulfide; and thiuram tetrasulfides such as dipentamethylenethiuram tetrasulfide. Examples of the thiocarboxylic acids include a naphthalene thiocarboxylic acid. Examples of the dithiocarboxylic acids include a naphthalene dithiocarboxylic acid. Examples of the sulfenamides include N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, and N-t-butyl-2-benzothiazole sulfenamide.
(e) The organic sulfur compound may be used solely or as a mixture of at least two of them.
The amount of (e) the organic sulfur compound is preferably 0.05 part by mass or more, more preferably 0.1 part by mass or more, and even more preferably 0.2 part by mass or more, and is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, and even more preferably 2.0 parts by mass or less, with respect to 100 parts by mass of (a) the rubber component. If the amount of (e) the organic sulfur compound falls within the above range, the processability is better to obtain a more homogenous rubber composition.
The rubber composition may further contain (f) a carboxylic acid and/or a metal salt thereof. As (f) the carboxylic acid and/or the metal salt thereof, a carboxylic acid having 1 to 30 carbon atoms and/or a metal salt thereof is preferable. As the carboxylic acid, an aliphatic carboxylic acid (a saturated fatty acid or an unsaturated fatty acid), or an aromatic carboxylic acid (e.g. benzoic acid) can be used. The amount of (f) the carboxylic acid and/or the metal salt thereof is preferably 1 part by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the rubber component.
The rubber composition may further contain an additive such as a filler for adjusting weight or the like, an antioxidant, a peptizing agent, and a softener, where necessary.
The filler blended in the rubber composition is mainly used as a weight adjusting agent for adjusting the weight of the golf ball obtained as a final product, and may be blended where necessary. Examples of the filler include an inorganic filler such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder. The amount of the filler is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, and is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, with respect to 100 parts by mass of the rubber component. If the amount of the filler is 0.5 part by mass or more, it is easier to adjust the weight, and if the amount of the filler is 30 parts by mass or less, the weight proportion of the rubber component increases and thus the durability tends to be better.
The amount of the antioxidant is preferably 0.1 part by mass or more and 1 part by mass or less with respect to 100 parts by mass of (a) the rubber component. In addition, the amount of the peptizing agent is preferably 0.1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of (a) the rubber component.
The rubber composition can be obtained by kneading (a) the rubber component, (b) the co-crosslinking agent, (c) the crosslinking initiator, and the other optional components. The kneading method is not particularly limited. For example, the kneading can be conducted with a conventional kneading machine such as a kneading roll, a banbury mixer and a kneader.
The spherical core can be molded, for example, by heat pressing the core rubber composition. The molding conditions for heat pressing the core rubber composition may be determined appropriately depending on the rubber composition. Generally, the heat pressing is preferably carried out at a temperature of 130° C. to 200° C. for 10 to 60 minutes, or carried out in a two-step heating of heating at a temperature of 130° C. to 150° C. for 20 to 40 minutes followed by heating at a temperature of 160° C. to 180° C. for 5 to 15 minutes.
The construction of the spherical core may be a single-layered construction, or a multi-layered construction, and the single-layered construction is preferable.
The diameter of the spherical core is preferably 34.8 mm or more, more preferably 36.8 mm or more, and even more preferably 38.0 mm or more, and is preferably 42.2 mm or less, more preferably 41.8 mm or less, even more preferably 41.2 mm or less, and most preferably 40.8 mm or less. If the diameter of the spherical core is 34.8 mm or more, the thickness of the cover is not excessively thick and thus the shot feeling is better. On the other hand, if the diameter of the spherical core is 42.2 mm or less, the thickness of the cover is not excessively thin and thus the cover functions better.
When the spherical core has a diameter in the range from 34.8 mm to 42.2 mm, the compression deformation amount of the spherical core (shrinking amount of the spherical core along the compression direction) when applying a load from an initial load of 98 N to a final load of 1275 N to the spherical core is preferably 2.0 mm or more, more preferably 2.5 mm or more, and even more preferably 3.0 mm or more, and is preferably 5.0 mm or less, more preferably 4.5 mm or less, and even more preferably 4.0 mm or less. If the compression deformation amount is 2.0 mm or more, the shot feeling on driver shots is better, and if the compression deformation amount is 5.0 mm or less, the durability is better.
The golf ball according to the present disclosure comprises a spherical core, at least one intermediate layer positioned outside the spherical core, and a cover positioned outside the intermediate layer. The cover is preferably single-layered. The cover positioned on the outermost side is sometimes referred to as an outermost cover. The single-layered cover corresponds to the outermost cover.
The construction of the golf ball according to the present disclosure is not particularly limited, as long as the golf ball comprises a spherical core, at least one intermediate layer positioned outside the spherical core, and a cover positioned outside the intermediate layer.
The figure is a partially cutaway cross-sectional view for illustrating one example of the golf ball according to the present disclosure. A golf ball 2 shown in the figure comprises a spherical core 4, an intermediate layer 6 covering the spherical core 4, and an outermost cover 8 positioned outside the intermediate layer 6. The golf ball 2 has a plurality of dimples 10 on the surface. Other portions than the dimples 10 on the surface of the golf ball 2 are lands 12. The golf ball 2 is provided with a paint layer and a mark layer on an outer side of the outermost cover 8, but these layers are not depicted.
Examples of the golf ball according to the present disclosure include a three-piece golf ball composed of a spherical core, a single-layered intermediate layer covering the spherical core, and a single-layered cover covering the intermediate layer; a multi-piece golf ball (including a three-piece golf ball, and the like) composed of a spherical core, one or more intermediate layers covering the spherical core, and a single-layered cover covering the intermediate layer. The present invention can be suitably applied to any one of the above golf balls. It is noted that the intermediate layer is sometimes referred to as an outer core or an inner cover depending on the construction of the golf ball.
(Cover composition and intermediate layer composition) The intermediate layer is preferably formed from an intermediate layer composition containing a resin component. The cover is preferably formed from a cover composition containing a resin component.
Examples of the resin component used in the resin composition for forming the cover and the intermediate layer include an ionomer resin, a urethane resin (a thermoplastic polyurethane elastomer, and a thermosetting polyurethane elastomer), a thermoplastic styrene elastomer, a thermoplastic polyamide elastomer, and a thermoplastic polyester elastomer.
Examples of the ionomer resin include a binary ionomer resin prepared by neutralizing at least a part of carboxyl groups in a binary copolymer composed of an olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms with a metal ion; a ternary ionomer resin prepared by neutralizing at least a part of carboxyl groups in a ternary copolymer composed of an olefin, an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α, β-unsaturated carboxylic acid ester with a metal ion; and a mixture of those.
Examples of the binary ionomer resin include Himilan (registered trademark) 1555 (Na), 1557 (Zn), 1605 (Na), 1706 (Zn), 1707 (Na), AM7311 (Mg), AM7329 (Zn), AM7337 (available from Dow-Mitsui Polychemicals Co., Ltd.); Surlyn (registered trademark) 8945 (Na), 9945 (Zn), 8140 (Na), 8150 (Na), 9120 (Zn), 9150 (Zn), 6910 (Mg), 6120 (Mg), 7930 (Li), 7940 (Li), AD8546 (Li) (available from E.I. du Pont de Nemours and Company); and lotek (registered trademark) 8000 (Na), 8030 (Na), 7010 (Zn), 7030 (Zn) (available from ExxonMobil Chemical Corporation).
Examples of the ternary ionomer resin include Himilan AM7327 (Zn), 1855 (Zn), 1856 (Na), AM7331 (Na) (available from Dow-Mitsui Polychemicals Co., Ltd.); Surlyn 6320 (Mg), 8120 (Na), 8320 (Na), 9320 (Zn), 9320W (Zn), HPF1000 (Mg), HPF2000 (Mg) (available from E.I. du Pont de Nemours and Company); and lotek 7510 (Zn), 7520 (Zn) (available from ExxonMobil Chemical Corporation). It is noted that Na, Zn, Li, Mg or the like described in the parentheses after the trade names of the ionomer resin indicate metal ion type for neutralizing the ionomer resin.
The thermoplastic polyurethane elastomer has a urethane bond in the molecule. The urethane bond may be formed by a reaction between a polyol and a polyisocyanate. The polyol which is the raw material for the urethane bond has a plurality of hydroxy groups, and a low molecular weight polyol or a high molecular weight polyol may be used.
Specific examples of the thermoplastic polyurethane elastomer include Elastollan (registered trademark) NY80A, NY84A, NY88A, NY95A, ET885, and ET890 (available from BASF Japan Ltd.).
As the thermoplastic styrene based elastomer, a thermoplastic elastomer containing a styrene block can be suitably used. The thermoplastic elastomer containing the styrene block has a polystyrene block that is a hard segment, and a soft segment.
The thermoplastic elastomer containing the styrene block includes a styrene-butadiene-styrene block copolymer (SBS), a styrene-isoprene-styrene block copolymer (SIS), a styrene-isoprene-butadiene-styrene block copolymer (SIBS), a hydrogenated product of SBS, a hydrogenated product of SIS, and a hydrogenated product of SIBS. Examples of the hydrogenated product of SBS include a styrene-ethylene-butylene-styrene block copolymer (SEBS). Examples of the hydrogenated product of SIS include a styrene-ethylene-propylene-styrene block copolymer (SEPS). Examples of the hydrogenated product of SIBS include a styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).
Examples of the thermoplastic styrene based elastomer include TEFABLOC T3221C, T3339C, SJ4400N, SJ5400N, SJ6400N, SJ7400N, SJ8400N, SJ9400N, and SR04 (available from Mitsubishi Chemical Corporation).
The cover composition constituting the cover preferably contains the polyurethane and/or the ionomer resin as the resin component, particularly preferably contains the polyurethane. If the cover contains the polyurethane as the resin component, the bite of the outermost cover into the club face on approach shots is greater, and thus the spin rate is easily increased.
When the cover composition contains the polyurethane as the resin component, the amount of the polyurethane in the resin component is preferably 50 mass % or more, more preferably 60 mass % or more, and even more preferably 70 mass % or more. The resin component of the cover composition may consist of the polyurethane (preferably the thermoplastic polyurethane elastomer).
When the cover composition contains the ionomer resin as the resin component, the amount of the ionomer resin in the resin component is preferably 50 mass % or more, more preferably 60 mass % or more, and even more preferably 70 mass % or more. When the ionomer resin is contained, the thermoplastic styrene elastomer is also preferably used in combination.
The intermediate layer composition preferably contains the ionomer resin as the resin component. When the ionomer resin is contained, the thermoplastic styrene elastomer is also preferably used in combination. The amount of the ionomer resin in the base resin of the intermediate layer composition is preferably 50 mass % or more, more preferably 60 mass % or more, and even more preferably 70 mass % or more.
The cover composition and the intermediate layer composition may contain a pigment component such as a white pigment (e.g. titanium oxide), a blue pigment and a red pigment, a weight adjusting agent such as zinc oxide, calcium carbonate and barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material or fluorescent brightener, or the like, in addition to the above resin component.
The amount of the white pigment (e.g. titanium oxide) is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, with respect to 100 parts by mass of the base resin constituting the outermost cover. If the amount of the white pigment is 0.5 part by mass or more, it is possible to impart the opacity to the cover. In addition, if the amount of the white pigment is 10 parts by mass or less, the obtained cover has better durability.
The method for molding the intermediate layer is not particularly limited, and examples thereof include a method which comprises molding the intermediate layer composition into a half shell in advance, covering the spherical core with two of the half shells, and performing compression molding; and a method which comprises injection molding the intermediate layer composition directly onto the spherical core to cover the spherical core.
Examples of the method for molding the cover include a method which comprises molding the cover composition into a hollow shell, covering the spherical body (the spherical core or the spherical body having the intermediate layer formed) with a plurality of the shells, and performing compression molding (preferably a method which comprises molding the cover composition into a hollow half-shell, covering the spherical body with two of the half-shells, and performing compression molding); and a method which comprises injection molding the cover composition directly onto the spherical body.
The golf ball body having the cover formed thereon is ejected from the mold, and is preferably subjected to surface treatments such as deburring, cleaning and sandblast where necessary.
The material hardness Hm of the intermediate layer composition constituting the intermediate layer is preferably 50 or more, more preferably 53 or more, and even more preferably 55 or more, and is preferably 75 or less, more preferably 73 or less, and even more preferably 71 or less in Shore D hardness. If the material hardness Hm is 50 or more, the flight distance is better due to the low spin rate on driver shots, and if the material hardness Hm is 75 or less, the shot feeling on driver shots is better. It is noted that in the case that the intermediate layer has a plurality of layers, the material hardness of the intermediate layer composition constituting the outermost intermediate layer is deemed as the material hardness Hm.
The thickness Tm of the intermediate layer is preferably 0.8 mm or more, more preferably 0.9 mm or more, and even more preferably 1.0 mm or more, and is preferably 3.0 mm or less, more preferably 2.6 mm or less, and even more preferably 2.2 mm or less. If the thickness Tm is 0.8 mm or more, the durability is better, and if the thickness Tm is 3.0 mm or less, better shot feeling on driver shots is obtained. It is noted that in the case that the intermediate layer has a plurality of layers, the total thickness of all the intermediate layers is deemed as the thickness Tm of the intermediate layer.
The material hardness Hc of the cover composition constituting the cover is preferably 20 or more, more preferably 22 or more, and even more preferably 24 or more, and is preferably 40 or less, more preferably 38 or less, and even more preferably 36 or less in Shore D hardness. If the material hardness Hc is 20 or more, the spin rate on driver shots is not excessively great, and thus the flight distance performance is better, and if the material hardness Hc is 40 or less, the spin performance on approach shots is better.
The thickness Tc of the cover is preferably 0.4 mm or more, more preferably 0.5 mm or more, and even more preferably 0.6 mm or more, and is preferably 1.0 mm or less, more preferably 0.9 mm or less, and even more preferably 0.8 mm or less. If the thickness Tc is 0.4 mm or more, the spin performance on approach shots is better, and if the thickness Tc is 1.0 mm or less, the spin rate on driver shots is not excessively great, and thus the flight distance performance is better.
The material hardness Hm of the intermediate layer is preferably greater than the material hardness Hc of the cover. The hardness difference (Hm-Hc) between the material hardness Hm of the intermediate layer and the material hardness Hc of the cover is preferably 20 or more, more preferably 22 or more, and even more preferably 24 or more, and is preferably 40 or less, more preferably 39 or less, and even more preferably 38 or less in Shore D hardness. If the hardness difference (Hm-Hc) falls within the above range, the shot feeling on driver shots is better.
In addition, if desired, a paint film or a mark may be formed. The thickness of the paint film is not particularly limited, and is preferably 5 μm or more, more preferably 6 μm or more, and even more preferably 7 μm or more, and is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. If the thickness of the paint film is 5 μm or more, the paint film is hard to wear off even if the golf ball is used continuously, and if the thickness of the paint film is 50 μm or less, the dimple effect is fully obtained. It is noted that the effect of the present disclosure is not impaired, since the paint film is very thin.
The golf ball according to the present disclosure preferably has a diameter ranging from 40 mm to 45 mm. In light of satisfying the regulation of US Golf Association (USGA), the diameter is particularly preferably 42.67 mm or more. In light of prevention of air resistance, the diameter is more preferably 44 mm or less, and particularly preferably 42.80 mm or less. In addition, the golf ball according to the present disclosure preferably has a mass of 40 g or more and 50 g or less. In light of obtaining greater inertia, the mass is more preferably 44 g or more, and particularly preferably 45.00 g or more. In light of satisfying the regulation of USGA, the mass is particularly preferably 45.93 g or less.
When the golf ball according to the present disclosure has a diameter in the range of from 40 mm to 45 mm, the compression deformation amount (shrinking amount along the compression direction) of the golf ball when applying a load from an initial load of 98 N to a final load of 1275 N to the golf ball is preferably 2.0 mm or more, more preferably 2.2 mm or more, and even more preferably 2.4 mm or more, and is preferably 3.5 mm or less, more preferably 3.3 mm or less, even more preferably 3.1 mm or less, and most preferably 2.8 mm or less. If the compression deformation amount is 2.0 mm or more, the golf ball is not excessively hard and thus has better shot feeling on driver shots. On the other hand, if the compression deformation amount is 3.5 mm or less, the durability is higher.
Next, the present disclosure will be described in detail by way of examples. However, the present disclosure is not limited to the examples described below. Various changes and modifications without departing from the spirit of the present disclosure are included in the scope of the present disclosure.
The compression deformation amount was measured with a YAMADA type compression tester “SCH”. The golf ball or core was placed on a metal rigid plate of the tester. A metal cylinder slowly fell toward the golf ball or core. The golf ball or core sandwiched between the bottom of the cylinder and the rigid plate deformed. The travelling distance of the cylinder when applying a load from an initial load of 98 N to a final load of 1275 N to the golf ball or core was measured. The compression deformation amount (mm) is the travelling distance. The travelling speed of the cylinder before applying the initial load was 0.83 mm/s. The travelling speed of the cylinder when applying the load from the initial load to the final load was 1.67 mm/s.
Sheets with a thickness of about 2 mm were produced by injection molding the intermediate layer composition or cover composition. The sheets were stored at a temperature of 23° C. for two weeks. At least three of these sheets were stacked on one another so as not to be affected by the measuring substrate on which the sheets were placed, and the hardness of the stack was measured with an automatic hardness tester (Digitest II, available from Bareiss company) using a testing device of “Shore D”.
An automatic hardness tester (Digitest II, available from Bareiss company) using a testing device of “Shore C” was used to measure the hardness. The Shore C hardness measured at the surface portion of the spherical core was adopted as the surface hardness of the spherical core. In addition, the spherical core was cut into two hemispheres along a plane passing through the center of the spherical core to obtain a cut plane, and the hardness at the central point of the cut plane and the hardness at the predetermined distance from the central point in the radius direction were measured. It is noted that each hardness was measured at four points, and the average value thereof was calculated.
(4) Ball Velocity (m/s), Spin Rate (Rpm) and Rolling Distance (m) on Approach (AP) Shot
Awedge “RTX3 BLD (loft angle: 58°)” available from Cleveland Golf Inc. was installed on a swing machine available from Golf Laboratories, Inc. The hitting point was set at the face center. The golf ball was hit at a head speed of 16 m/see, and the ball velocity (m/s) and the backspin rate (rpm) right after hitting the golf ball, and the rolling distance (m) (the distance from the fall point to the stop point) were measured. The ball velocity and the backspin rate were measured by continuously taking a sequence of photographs of the golf ball right after hitting the golf ball. The measurement was conducted twelve times for each golf ball, and the average value of the obtained data was adopted as the measurement value for that golf ball.
Awedge “RTX3 BLD (loft angle: 58°)” available from Cleveland Golf Inc. was used by 20 golfers to conduct an actual hitting on a 20-yard approach shot, and the shot feeling was evaluated according to the following evaluation standard.
Evaluation standard
According to the formulations shown in Table 1, the materials were kneaded with a kneading roll to obtain the core compositions.
*1)The amount of barium sulfate was adjusted such that the golf balls had a mass of 45.3 g.
The materials used in Table 1 are shown as follows.
According to the formulations shown in Table 2, the materials were extruded with a twin-screw kneading type extruder to prepare the intermediate layer compositions in a pellet form.
Surlyn (registered trademark) 8150: sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin available from E.I. du Pont de Nemours and Company.
Himilan (registered trademark) 1605: sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin available from Dow-Mitsui Polychemicals Co., Ltd.
Himilan (registered trademark) AM7329: sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin available from Dow-Mitsui Polychemicals Co., Ltd.
Himilan (registered trademark) 1555: sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin available from Dow-Mitsui Polychemicals Co., Ltd.
Himilan (registered trademark) 1557: zinc ion neutralized ethylene-methacrylic acid copolymer ionomer resin available from Dow-Mitsui Polychemicals Co., Ltd.
TEFABLOC T3221C: thermoplastic styrene based elastomer available from Mitsubishi Chemical Corporation
Titanium dioxide: A-220 available from Ishihara Sangyo Kaisha, Ltd.
According to the formulations shown in Table 3, the materials were extruded with a twin-screw kneading type extruder to prepare the cover compositions in a pellet form.
Elastollan (registered trademark) NY80A: thermoplastic polyurethane elastomer available from BASF Japan Ltd.
Elastollan (registered trademark) NY84A: thermoplastic polyurethane elastomer available from BASF Japan Ltd.
Elastollan (registered trademark) NY88A: thermoplastic polyurethane elastomer available from BASF Japan Ltd.
Elastollan (registered trademark) NY95A: thermoplastic polyurethane elastomer available from BASF Japan Ltd.
Tinuvin (registered trademark) 770: hindered amine-based light stabilizer available from BASF Japan Ltd.
Titanium dioxide: A-220 available from Ishihara Sangyo Kaisha, Ltd.
The core compositions shown in Table 1 were heat-pressed in upper and lower molds, each having a hemispherical cavity, to obtain the spherical cores. It is noted that barium sulfate was added in an appropriate amount such that the obtained golf balls had a mass of 45.3 g.
The intermediate layer composition was injection molded on the spherical core to obtain the intermediate layer-covering spherical body. The obtained intermediate layer-covering spherical body was charged into a final mold provided with a plurality of pimples on the cavity surface. Half shells were obtained from the cover composition by a compression molding method. The intermediate layer-covering spherical body charged into the final mold was covered with two of the half shells to obtain the golf balls having an outermost cover on which a plurality of dimples with an inverted shape of the pimple shape on the cavity surface were formed. The evaluation results regarding the obtained golf balls are shown in Tables 4 to 6.
It is apparent from the results shown in Tables 4 to 6 that the golf ball according to the present disclosure that comprises a spherical core, at least one intermediate layer positioned outside the spherical core, and a cover positioned outside the intermediate layer, wherein the spherical core is formed from a rubber composition containing a rubber component, a co-crosslinking agent, and a crosslinking initiator, the co-crosslinking agent contains methacrylic acid and/or a metal salt thereof, and when a center hardness (Shore C hardness) of the spherical core, a hardness (Shore C hardness) at each point of 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12.5 mm and 15 mm from a center of the spherical core toward a surface of the spherical core, and a surface hardness (Shore C hardness) of the spherical core are represented by H0, H2.5, H5, H7.5, H10, H12.5, H15, HS respectively, the following relationship is satisfied, has a low initial velocity on approach shots, rolls a short distance, has excellent controllability and a good shot feeling on approach shots.
H0<H2.5<H5<H7.5<H10<H12.5<H15<HS
The golf ball according to the present disclosure shows a low initial velocity on approach shots, rolls a short distance, and has excellent controllability. In addition, the golf ball according to the present disclosure has a good shot feeling on approach shots.
The preferable embodiment (1) according to the present disclosure is a golf ball comprising a spherical core, at least one intermediate layer positioned outside the spherical core, and a cover positioned outside the intermediate layer, wherein
H0<H2.5<H5<H7.5<H10<H12.5<H15<HS.
The preferable embodiment (2) according to the present disclosure is the golf ball according to the embodiment (1), wherein each of (H2.5−H0), (H5−H2.5), (H7.5-H5), (H10−H7.5), (H12.5−H10), (H15−H12.5), and (HS−H15) is 5 or less.
The preferable embodiment (3) according to the present disclosure is the golf ball according to the embodiment (1) or (2), wherein (HS−H0) is 20 or less.
The preferable embodiment (4) according to the present disclosure is the golf ball according to any one of the embodiments (1) to (3), wherein the surface hardness HS of the spherical core is 80 or less in Shore C hardness, and the center hardness H0 of the spherical core is 60 or less in Shore C hardness.
The preferable embodiment (5) according to the present disclosure is the golf ball according to any one of the embodiments (1) to (4), wherein a material hardness Hm of the intermediate layer is greater than a material hardness Hc of the cover.
The preferable embodiment (6) according to the present disclosure is the golf ball according to any one of the embodiments (1) to (5), wherein the intermediate layer has a material hardness Hm of 50 or more in Shore D hardness.
The preferable embodiment (7) according to the present disclosure is the golf ball according to any one of the embodiments (1) to (6), wherein the cover has a material hardness Hc of 40 or less in Shore D hardness.
The preferable embodiment (8) according to the present disclosure is the golf ball according to any one of the embodiments (1) to (7), wherein the rubber component is a mixture of a polybutadiene and a butyl rubber and/or an isoprene rubber.
The preferable embodiment (9) according to the present disclosure is the golf ball according to any one of the embodiments (1) to (8), wherein the intermediate layer contains an ionomer resin as a resin component.
The preferable embodiment (10) according to the present disclosure is the golf ball according to any one of the embodiments (1) to (9), wherein the cover contains a polyurethane as a resin component.
This application is based on Japanese patent application No. 2023-127130 filed on Aug. 3, 2023, the content of which is hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-127130 | Aug 2023 | JP | national |
