Multi-piece solid golf ball

Abstract

To provide a golf ball with which, in order to attain the conformity to new overall distance standard (ODS) rules, a driving distance in a case where an amateur user performs a full shot can be satisfactorily maintained without a fall, the amateur user can easily raise a ball in the case of an approach, and a hitting feeling with a soft feeling and a bouncing feeling is applied.SOLUTION: A multi-piece solid golf ball comprises a core, an enclosure layer, an intermediate layer and a cover and a number of dimples are formed on an outer surface of the cover. A relation of surface hardness of each ball body is specified, and an initial speed of the ball is set to 75.0 to 77.724 m / s. A relation of ratios with respect to a lift coefficient / drag coefficient in a Reynolds number of 218,000 and a spin rate of 2,800 rpm, a lift coefficient / drag coefficient in a Reynolds number of 184,000 and a spin rate of 2,900 rpm and a lift coefficient / drag coefficient in a Reynolds number of 158,000 and a spin rate of 3,100 rpm is specified.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multi-piece solid golf ball that conforms to the new Overall Distance Standard (ODS) rules that will be applied from January 2028 onwards, while offering good distance for amateur players and making it easy to lift the ball on approach shots, making the golf game easier. [Background technology]

[0002] In March 2022, the R&A and the USGA notified golf ball manufacturers that they would begin research into limiting the distances of longest hitters by changing the test conditions for golf ball overall distance standards (ODS).Furthermore, in December 2023, the R&A and the USGA made the following specific announcements: "The club head speed for the overall standard distance (ODS) for conforming to the rules will be increased from the current 54 m / s to 56 m / s. This is expected to have an impact of 13 to 15 yards (11.9 to 13.7 m) on the hitting conditions of longest hitters." The testing changes will come into effect in January 2028, but will remain available for non-competitive recreational golf until January 1, 2030.

[0003] Therefore, the time is approaching when a ball with a reduced distance compared to current balls will be required under the hitting conditions of long hitters with high head speeds. On the other hand, for golf balls aimed at amateur users, even if the reduced distance is mentioned above, it is desirable for the ball to have as long a distance as possible under the hitting conditions of the amateur user's head speed. Furthermore, since non-competitive amateur users find it difficult to lift the ball on approach shots, a ball that is easy to lift on approach shots, i.e., a high launch angle, is likely to be perceived as an "easy-to-use ball for approach shots." Furthermore, amateur users prefer a ball that is soft yet has a bouncy feel and a shot that seems to fly. It is desirable to develop a ball that satisfies all of these characteristics simultaneously for amateur users.

[0004] Additionally, in the past, several golf balls have been proposed that have an initial velocity set lower than that of ordinary game balls. Examples of such technical documents include the following Patent Documents 1 to 5.

[0005] However, all of the golf balls proposed above are practice balls for driving ranges that are simply designed to have a shorter flight distance than game balls. Therefore, the above patent documents do not consider at all the good flight distance performance when hit by amateur users, the ease of lifting the ball when approaching, and the feel of the ball when hit.

[0006] Furthermore, for dimples formed on the surface of the ball, the total volume of the dimples formed below the plane surrounded by the edges of the dimples is the volume of the ball assuming no dimples existed, i.e., the dimple volume ratio VR is specified within a predetermined range, and examples of golf balls that can achieve advantageous distances in low head speed (HS) areas while suppressing distances in high head speed (HS) areas include Patent Documents 6 to 14 listed below.

[0007] However, the golf balls proposed above suffer from a significant decrease in flight distance at high head speeds, and the flight distance achieved by amateur players on full shots is also unsatisfactory. Furthermore, the above patent documents do not take into consideration the ease of lifting the ball and the feel of the ball when approaching. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-228470 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-069045 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-138857 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-138839 [Patent Document 5] Japanese Patent Application Laid-Open No. 2013-138840 [Patent Document 6] Japanese Patent Application Laid-Open No. 2011-218160 [Patent Document 7] Japanese Patent Application Laid-Open No. 2011-218161 [Patent Document 8] Japanese Patent Application Laid-Open No. 2011-218162 [Patent Document 9] Japanese Patent Application Laid-Open No. 2011-240122 [Patent Document 10] Japanese Patent Application Laid-Open No. 2011-240123 [Patent Document 11] Japanese Patent Application Laid-Open No. 2011-240124 [Patent Document 12] Japanese Patent Application Laid-Open No. 2011-240125 [Patent Document 13] Japanese Patent Application Laid-Open No. 2011-240126 [Patent Document 14] Japanese Patent Application Laid-Open No. 2011-240127 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide a multi-piece solid golf ball that is designed to comply with the new Overall Distance Standard (ODS) rules that will come into effect from January 2028 onwards, and that not only reduces the flight distance when hit by a longest hitter to a certain level or more, but also allows amateur users to maintain a good flight distance when hitting full shots with a driver (W#1) or iron, without any reduction in flight distance, and furthermore, increases the launch angle when amateur users approach, making it easier to lift the ball, and has a bouncy feel that makes it seem like the ball will fly. [Means for solving the problem]

[0010] As a result of extensive research into achieving the above object, the present inventors have discovered a multi-piece solid golf ball having a core, an envelope layer, an intermediate layer, and a cover, with numerous dimples formed on the outer surface of the cover, wherein the core is made of a rubber material, and the envelope layer, intermediate layer, and cover are made of a resin material, and the relationship between the surface hardness of the ball, envelope layer-covered sphere, and intermediate layer-covered sphere is expressed by the following formula (1-a) and the following formula (1-b): (Surface hardness of ball) > (Surface hardness of envelope-coated sphere) (1-a) (Surface hardness of ball) > (Surface hardness of intermediate layer-coated ball) (1-b) The relationship between the surface hardness of the core, the envelope layer-coated sphere, and the intermediate layer-coated sphere is expressed by the following formula (2-a) or (2-b): (Surface hardness of the envelope-coated sphere) < (Surface hardness of the core) (2-a) (Surface hardness of intermediate layer coated sphere) < (Surface hardness of core) (2-b) The initial velocity of the ball is set to a range of 75.0 to 77.724 m / s, and the ratio CL1 / CD1 of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm is defined as A1, the ratio CL2 / CD2 of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm is defined as A2, and the ratio CL3 / CD3 of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm is defined as A3. Then, the following two equations are satisfied: 0.590≦A1≦0.655, and (A2+A3) / 2≧0.670 and the volume fraction VR of the dimples is 0.75 to 0.89%, and the total volume of the dimples is D (mm 3 ), the amount of deflection when the ball is loaded from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is B (mm), and the following formula is used: 95≦D / B≦140 It has been discovered that by designing a multi-piece solid golf ball to satisfy the above, it is possible to achieve compliance with the new Overall Distance Standard (ODS) rules, i.e., the reduction in flight distance when hit by a longest hitter occurs above a certain level, and the flight distance when an amateur user hits a full shot with a driver (W#1) or iron does not decrease but rather increases. Furthermore, with the above-designed multi-piece solid golf ball, the launch angle of the ball when an amateur user approaches is high, making it easier to lift the ball, resulting in a ball that is "easy to approach," and further, when an amateur user hits a full shot, it has a feel that is both soft and bouncy, giving the impression of flying. This has led to the present invention.

[0011] The above-mentioned "longest hitter" refers to a golfer whose head speed when hitting with a driver (W#1) is 50 m / s or more, and the above-mentioned "non-competitive amateur golfer" refers to a golfer whose head speed when hitting with a driver (W#1) is 45 m / s or less and whose handicap, if any, is approximately 30 or more.

[0012] Accordingly, the present invention provides the following multi-piece solid golf ball. 1. A multi-piece solid golf ball comprising a core, a single or multiple envelope layer, a single intermediate layer, and a single cover, with numerous dimples formed on the outer surface of the cover, wherein the core is made of a rubber material, and the envelope layer, intermediate layer, and cover are made of a resin material, and the relationship between the surface hardness of the ball, envelope layer-covered sphere, and intermediate layer-covered sphere satisfies the following formula (1-a) and the following formula (1-b): (Surface hardness of ball) > (Surface hardness of envelope-coated sphere) (1-a) (Surface hardness of ball) > (Surface hardness of intermediate layer-coated ball) (1-b) (However, hardness refers to Shore C hardness.) The relationship between the surface hardness of the core, the envelope layer-coated sphere, and the intermediate layer-coated sphere satisfies the following formula (2-a) or the following formula (2-b): (Surface hardness of the envelope-coated sphere) < (Surface hardness of the core) (2-a) (Surface hardness of intermediate layer coated sphere) < (Surface hardness of core) (2-b) (However, hardness refers to Shore C hardness.) When at least one of the following equations is satisfied, and the initial velocity of the ball is between 75.0 and 77.724 m / s, and the ratio CL1 / CD1 of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm is A1, the ratio CL2 / CD2 of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm is A2, and the ratio CL3 / CD3 of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm is A3, then the following two equations are satisfied: 0.590≦A1≦0.655, and (A2+A3) / 2≧0.670 and the volume fraction VR of the dimples is 0.75 to 0.89%, and the total volume of the dimples is D (mm 3 ), the amount of deflection when the ball is loaded from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is B (mm), and the following formula is used: 95≦D / B≦140 A multi-piece solid golf ball characterized by satisfying the above. 2. The multi-piece solid golf ball according to 1 above, wherein the value of A1 is 0.590 to 0.613, the value of A2 is 0.635 to 0.668, and the value of A3 is 0.695 to 0.734. 3. The multi-piece solid golf ball according to 1 above, wherein the value of A1 is 0.614 to 0.655, the value of A2 is 0.669 to 0.750, and the value of A3 is 0.735 to 0.815. 4. The multi-piece solid golf ball according to 1 or 2 above, wherein the value of (A2+A3) / 2 is 0.670 to 0.783. 5. The multi-piece solid golf ball according to 1 or 2 above, wherein the cover is formed primarily from an ionomer resin. 6. The relationship between the surface hardness of each sphere is as follows: (Surface hardness of ball) > (Surface hardness of mid-layer coated ball) > (Surface hardness of envelope coated ball) < (Surface hardness of core) (However, hardness refers to Shore C hardness.) 3. A multi-piece solid golf ball according to 1 or 2 above, which satisfies the above conditions. 7. In the hardness distribution of the core described above, the Shore C hardness at the center of the core is Cc, the Shore C hardness at the midpoint M between the center and the surface of the core is Cm, the Shore C hardnesses at 2mm, 4mm, and 6mm inward from the midpoint M are Cm-2, Cm-4, and Cm-6, respectively, the Shore C hardnesses at 2mm, 4mm, and 6mm outward from the midpoint M are Cm+2, Cm+4, and Cm+6, respectively, and the Shore C hardness of the surface of the core is Cs. The following areas A to F are then calculated. ·Area A: 1 / 2×2×(Cm-4-Cm-6) ·Area B: 1 / 2×2×(Cm-2-Cm-4) ·Area C: 1 / 2×2×(Cm-Cm-2) ·Area D: 1 / 2×2×(Cm+2-Cm) ·Area E: 1 / 2×2×(Cm+4-Cm+2) ·Area F: 1 / 2×2×(Cm+6-Cm+4) Regarding {(Area D+Area E)-(Area A+Area B)}≧4.0 3. A multi-piece solid golf ball according to 1 or 2 above, which satisfies the above conditions. 8. In the hardness distribution of the above core, the following formula (Cs-Cc)≧20 7. A multi-piece solid golf ball according to claim 7, which satisfies the above requirements. 9. In the hardness distribution of the above core, the following formula (Cs-Cc) / (Cm-Cc)≧4.0 7. A multi-piece solid golf ball according to claim 7, which satisfies the above requirements. 10. In the hardness distribution of the core, the following formula Area E > Area D > Area C 7. A multi-piece solid golf ball according to claim 7, which satisfies the above requirement. 11. The core comprises the following components (A) to (D): (A) Base rubber (B) Organic peroxide (C) Water or a metal monocarboxylate (D) Sulfur 3. The multi-piece solid golf ball according to 1 or 2 above, which is formed from a rubber composition containing [Effects of the Invention]

[0013] The multi-piece solid golf ball of the present invention is a golf ball that conforms to the new Overall Distance Standard (ODS) rules that will come into effect after January 2028. While reducing the distance when hit with a driver by longest hitters, it does not reduce the distance when amateur users hit full shots with a driver (W#1) or iron, and in fact can increase the distance. Furthermore, the golf ball of the present invention increases the launch angle of the ball when an amateur user approaches, making it easier to lift the ball and providing a feeling of ease when approaching. Furthermore, the golf ball of the present invention provides a feel that is both soft and likely to fly when an amateur user hits a full shot. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view of a multi-piece solid golf ball (four-layer structure) of the present invention. [Figure 2] FIG. 1 is a schematic diagram illustrating areas A to F of the core hardness distribution, using core hardness distribution data of Example 1. [Figure 3] 1 is a graph showing the core hardness distribution of Examples 1 to 4 and Comparative Examples 1 to 5. [Figure 4] 1 is a graph showing the core hardness distribution of Comparative Examples 6 to 15. [Figure 5] 1 shows the arrangement (pattern) of dimples (1) to (5) used in Examples 1 to 4 and Comparative Examples 1 to 15, where (A) shows a plan view of the dimples and (B) shows a side view thereof.

[0015] The present invention will be described in more detail below. The multi-piece solid golf ball of the present invention has a core, an envelope layer, a mid layer, and a cover, an example of which is shown in FIG. 1. The golf ball G shown in FIG. 1 has a single-layer core 1, a single-layer envelope layer 2 enclosing the core, a single-layer intermediate layer 3 enclosing the envelope layer, and a single-layer cover 4 enclosing the intermediate layer. The cover 4 is the outermost layer of the golf ball's layer structure, excluding the paint layer. Each of the core and envelope layer can be formed as a single layer as shown in FIG. 1, or as multiple layers. Numerous dimples D are formed on the surface of the cover (outermost layer) 4 to achieve the aerodynamic characteristics targeted by the present invention. Although not specifically shown, a paint layer is typically formed on the surface of the cover 2. Each of the above layers is described in detail below.

[0016] The core is obtained by vulcanizing a rubber composition primarily made of rubber. If the core material is not a rubber composition, the core's resilience will be low, and not only long hitters but also amateur users may not be able to achieve the desired distance when hitting with a driver (W#1) or iron. This rubber composition is usually made primarily from a base rubber, to which a co-crosslinking agent, a crosslinking initiator, an inert filler, an organic sulfur compound, etc. are compounded to obtain the rubber composition.

[0017] The core may particularly comprise the following components (A) to (D): (A) Base rubber (B) Organic peroxide (C) Water or a metal monocarboxylate (D) Sulfur It is preferable that the rubber composition contains the above-mentioned compound.

[0018] The base rubber (A) may contain a diene rubber, such as polybutadiene, natural rubber, isoprene rubber, or ethylene propylene diene rubber.

[0019] As the (B) organic peroxide, it is preferable to use an organic peroxide with a relatively high thermal decomposition temperature. Specifically, an organic peroxide with a 1-minute half-life temperature of approximately 165 to 185°C is used, and examples thereof include dialkyl peroxides. Examples of dialkyl peroxides include dicumyl peroxide (NOF Corp.'s "Percumyl D"), 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (NOF Corp.'s "Perhexa 25B"), and di(2-t-butylperoxyisopropyl)benzene (NOF Corp.'s "Perbutyl P"), with dicumyl peroxide being preferred. These may be used alone or in combination. The half-life is an index of the decomposition rate of an organic peroxide and is expressed as the time required for the original organic peroxide to decompose and reduce its active oxygen content by half. The vulcanization temperature for the core rubber composition is usually within the range of 120 to 190°C, and within this range, organic peroxides, which have a high one-minute half-life temperature of approximately 165 to 185°C, thermally decompose relatively slowly. With the rubber composition used in the present invention, it is possible to obtain a core, which is a cross-linked rubber product having a specific internal hardness profile, as described below, by adjusting the amount of free radicals produced, which increases with the passage of vulcanization time.

[0020] The water (C) is not particularly limited and may be distilled water or tap water, but it is particularly preferred to use distilled water that does not contain impurities. The amount of water blended is preferably 0.1 part by weight or more, more preferably 0.2 part by weight or more, per 100 parts by weight of the base rubber, and the upper limit is preferably 2 parts by weight or less, more preferably 1 part by weight or less.

[0021] By directly blending water or a water-containing material as component (C) into the core material, the decomposition of organic peroxides during core compounding can be accelerated. It is known that the decomposition efficiency of organic peroxides in core rubber compositions varies with temperature, with the decomposition efficiency increasing as the temperature rises. If the temperature is too high, too many radicals are decomposed, leading to recombination and inactivation of the radicals. As a result, the number of radicals available for crosslinking is reduced. When the organic peroxide decomposes during core vulcanization and generates heat, the temperature near the core surface remains roughly the same as the vulcanization mold temperature. However, the temperature near the core center rises significantly higher than the mold temperature due to the accumulation of heat from the decomposition of the organic peroxide decomposed from the outside. When water or a water-containing material is directly blended into the core, the water promotes the decomposition of the organic peroxide, thereby altering the radical reaction described above between the core center and the core surface. That is, near the core center, the decomposition of the organic peroxide is further promoted, and the deactivation of radicals is further promoted, further reducing the amount of effective radicals. This makes it possible to obtain cores with significantly different crosslink densities between the core center and the core surface, and cores with different dynamic viscoelastic properties in the core center.

[0022] Alternatively, a monocarboxylate metal salt can be used instead of the water described above. It is believed that a carboxylic acid is coordinately bonded to the metal salt in a monocarboxylate metal salt, and it is distinct from dicarboxylate metal salts such as zinc diacrylate, which has the chemical formula [CH₂=CHCOO]₂Zn. A monocarboxylate metal salt introduces water into the rubber composition through a dehydration condensation reaction, thereby achieving the same effects as water. Furthermore, a monocarboxylate metal salt can be incorporated into the rubber composition as a powder, simplifying the processing steps and facilitating uniform dispersion throughout the rubber composition. To effectively carry out the reaction, a monosalt is required. The amount of the monocarboxylate metal salt is preferably 1 part by weight or more, more preferably 3 parts by weight or more, per 100 parts by weight of the base rubber. The upper limit of the amount of the monocarboxylate metal salt is preferably 60 parts by weight or less, more preferably 50 parts by weight or less. If the amount of the monocarboxylate metal salt is too small, it may be difficult to achieve an appropriate crosslink density, which may result in an insufficient golf ball spin reduction effect. On the other hand, if the blending amount is too high, the core becomes too hard, which may make it difficult to maintain an appropriate feel on impact.

[0023] Examples of the carboxylic acid that can be used include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and stearic acid. Examples of the substituting metal include Na, K, Li, Zn, Cu, Mg, Ca, Co, Ni, and Pb, with Zn being preferred. Specific examples include zinc monoacrylate and zinc monomethacrylate, with zinc monoacrylate being particularly preferred.

[0024] Specific examples of (D) sulfur include products such as "Sunmix S-80N" (manufactured by Sanshin Chemical Industry Co., Ltd.) and "Sulfax-5" (manufactured by Tsurumi Chemical Industry Co., Ltd.). The amount of sulfur can be greater than 0, preferably at least 0.005 parts by weight, and more preferably at least 0.01 parts by weight, per 100 parts by weight of the base rubber. There is no upper limit to the amount of sulfur added, but it is preferably no more than 0.1 parts by weight, more preferably no more than 0.05 parts by weight, and even more preferably no more than 0.03 parts by weight. The addition of sulfur can increase the hardness difference in the core. However, if the amount of sulfur added is too high, the resilience may be significantly reduced and durability against repeated impacts may be reduced.

[0025] The rubber composition may contain other components besides the components (A) to (D), such as a co-crosslinking agent, a filler, an antioxidant, and an organic sulfur compound.

[0026] The co-crosslinking agent is an α,β-unsaturated carboxylic acid and / or a metal salt thereof. Specific examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, and fumaric acid, with acrylic acid and methacrylic acid being particularly preferred. Metal salts of unsaturated carboxylic acids are not particularly limited, but examples include those obtained by neutralizing the above-mentioned unsaturated carboxylic acids with desired metal ions. Specific examples include zinc salts and magnesium salts of methacrylic acid, acrylic acid, and the like, with zinc acrylate being particularly preferred.

[0027] The unsaturated carboxylic acid and / or metal salt thereof is blended in an amount of typically 5 parts by weight or more, preferably 9 parts by weight or more, and more preferably 13 parts by weight or more, per 100 parts by weight of the base rubber, with the upper limit typically being 60 parts by weight or less, preferably 50 parts by weight or less, and more preferably 40 parts by weight or less. If the blended amount is too high, the ball may become too hard, resulting in an unbearable feel at impact, while if the blended amount is too low, the resilience may decrease.

[0028] Suitable fillers include, for example, zinc oxide, barium sulfate, and calcium carbonate. These may be used alone or in combination. The amount of filler added is preferably at least 4 parts by weight, more preferably at least 8 parts by weight, and even more preferably at least 11 parts by weight per 100 parts by weight of the base rubber. The upper limit of this amount is preferably no more than 50 parts by weight, more preferably no more than 40 parts by weight, and even more preferably no more than 35 parts by weight per 100 parts by weight of the base rubber. If the amount added is too high or too low, it may be difficult to achieve the appropriate mass and appropriate resilience.

[0029] As the antioxidant, for example, commercially available products such as Nocrac NS-6, Nocrac NS-30, Nocrac 200, Nocrac MB (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) can be used. These may be used alone or in combination of two or more.

[0030] The amount of antioxidant blended is not particularly limited, but is preferably at least 0.05 part by weight, more preferably at least 0.1 part by weight, and preferably not more than 1.0 part by weight, more preferably not more than 0.7 part by weight, and even more preferably not more than 0.5 part by weight, per 100 parts by weight of base rubber. If the blended amount is too high or too low, the appropriate core hardness gradient may not be obtained, and favorable resilience, durability, and spin reduction effect on full shots may not be achieved.

[0031] The organic sulfur compound can be blended to control the core's resilience.Specific examples of the organic sulfur compound include thiophenol, thionaphthol, halogenated thiophenol, and their metal salts.More specifically, examples include zinc salts of pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, pentachlorothiophenol, and the like, and diphenyl polysulfide, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, dithiobenzoyl polysulfide, and the like, which have 2 to 4 sulfur atoms.In particular, the zinc salt of pentachlorothiophenol and diphenyl disulfide can be preferably used.

[0032] The upper limit of the amount of organic sulfur compound per 100 parts by weight of the base rubber is preferably no more than 5 parts by weight, more preferably no more than 4 parts by weight, even more preferably no more than 3 parts by weight, and most preferably no more than 2 parts by weight. If this amount is too high, the core may become too soft or the core may have too high resilience, resulting in excessive distance for long hitters when hitting with a driver.

[0033] The core can be produced by vulcanizing and curing a rubber composition containing the above components. For example, the core can be produced by kneading the rubber composition using a kneader such as a Banbury mixer or a roll, compression molding or injection molding using a core mold, and curing the molded product by appropriately heating the molded product at a temperature sufficient for the organic peroxide and co-crosslinking agent to act, 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes.

[0034] In the present invention, the core may be formed of a single layer or multiple layers, but a single layer is preferred. If a rubber core is formed of multiple layers, repeated impacts may cause peeling at the interface, resulting in early cracking.

[0035] The core diameter is preferably 32.7 mm or more, more preferably 34.3 mm or more, and even more preferably 34.9 mm or more. The upper limit of this diameter is preferably 36.5 mm or less, more preferably 36.1 mm or less, and even more preferably 35.7 mm or less. If the core diameter is too small, the initial velocity of the ball may be too low, or the overall deflection of the ball may be reduced, increasing the spin rate on full shots and preventing amateur users from achieving the desired distance on full shots. On the other hand, if the core diameter is too large, the spin rate on full shots may be increased, preventing amateur users from achieving the desired distance, or the durability to cracking may be reduced when hit repeatedly.

[0036] The deflection (mm) of the core when subjected to an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is not particularly limited, but is preferably at least 3.6 mm, more preferably at least 4.0 mm, and even more preferably at least 4.3 mm. The upper limit is preferably at most 5.5 mm, more preferably at most 5.2 mm, and even more preferably at most 4.9 mm. If the core deflection is too small, i.e., if the core is too hard, the spin rate on full shots may increase too much, resulting in a loss of distance when amateur users hit the ball with a driver (W#1) or an iron, and the feel may be too hard. On the other hand, if the core deflection is too large, i.e., if the core is too soft, the initial velocity may be too low, resulting in a significant loss of distance when longest hitters and amateur users hit the ball with a driver (W#1). The feel may be less bouncy and the ball may not fly, and the durability to cracking may be too poor when hit repeatedly.

[0037] Next, the hardness distribution of the core will be described. Note that the hardness of the core described below refers to Shore C hardness. This Shore C hardness is a hardness value measured using a Shore C hardness tester conforming to the ASTM D2240 standard.

[0038] The center hardness (Cc) of the core is preferably 50 or greater, more preferably 52 or greater, and even more preferably 54 or greater, with the upper limit being preferably 62 or less, more preferably 59 or less, and even more preferably 56 or less. If this value is too high, the spin rate on full shots will be high, preventing amateur users from achieving the desired distance when hitting with a driver (W#1) or an iron, or the feel on impact may be too hard. On the other hand, if this value is too low, the resilience will be low, preventing amateur users from achieving the desired distance, causing a lack of bounce and a loss of the feeling of distance, or the durability to cracking when hit repeatedly may be poor.

[0039] The hardness (Cm-6) measured at a position 6 mm inward from the midpoint M between the center and the surface of the core (hereinafter also referred to as "midpoint M") is not particularly limited, but is preferably at least 51, more preferably at least 53, and even more preferably at least 55. There is no upper limit to this value, but it is preferably at most 63, more preferably at most 60, and even more preferably at most 57. Hardnesses that deviate from these limits may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0040] The hardness (Cm-4) at a position 4 mm inward from a position M midway between the center and the surface of the core (hereinafter also referred to as "midpoint M") is not particularly limited, but is preferably at least 51, more preferably at least 53, and even more preferably at least 55. There is no upper limit to this hardness, but it is preferably at most 63, more preferably at most 60, and even more preferably at most 57. Hardnesses that deviate from these limits may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0041] The hardness (Cm-2) at a position 2 mm inward from the center position M of the core is not particularly limited, but is preferably at least 53, more preferably at least 55, and even more preferably at least 57. There is no upper limit to this hardness, but it is preferably at most 64, more preferably at most 61, and even more preferably at most 59. Hardnesses that deviate from these limits may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0042] The cross-sectional hardness (Cm) of the core at the center position M is not particularly limited, but is preferably at least 54, more preferably at least 56, and even more preferably at least 58. There is also no particular upper limit, but it is preferably at most 66, more preferably at most 63, and even more preferably at most 60. Hardnesses outside these limits may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0043] The surface hardness (Cs) of the core is preferably 70 or higher, more preferably 72 or higher, and even more preferably 74 or higher, with the upper limit being preferably 82 or lower, more preferably 79 or lower, and even more preferably 77 or lower. If this value is too high, durability to cracking during repeated impacts may be poor, or the feel on impact may be too hard. On the other hand, if this value is too low, the resilience may be low, or the spin rate on full shots may be high, preventing amateur users from achieving the desired distance when hitting with a driver (W#1) or an iron.

[0044] The hardness (Cm+2) at a position 2 mm outward from the center position M of the core toward the core surface (hereinafter simply referred to as the "outside") is not particularly limited, but is preferably 59 or greater, more preferably 61 or greater, and even more preferably 63 or greater. There is no upper limit to this hardness, but it is preferably 70 or less, more preferably 67 or less, and even more preferably 65 or less. Hardnesses that deviate from these limits may result in the same adverse effects as those described above for the surface hardness (Cs) of the core.

[0045] The hardness (Cm+4) at a position 4 mm outward from the center position M of the core is not particularly limited, but is preferably at least 63, more preferably at least 65, and even more preferably at least 67. There is no upper limit to this hardness, but it is preferably at most 74, more preferably at most 72, and even more preferably at most 70. Hardnesses that deviate from these limits may result in the same adverse effects as those described for the surface hardness (Cs) of the core.

[0046] The hardness (Cm+6) at a position 6 mm outward from the center position M of the core is not particularly limited, but is preferably at least 64, more preferably at least 66, and even more preferably at least 68. There is no upper limit to this hardness, but it is preferably at most 75, more preferably at most 73, and even more preferably at most 71. Hardnesses that deviate from these limits may result in the same adverse effects as those described for the surface hardness (Cs) of the core.

[0047] The value obtained by subtracting the center hardness from the surface hardness of the core, i.e., the Cs-Cc value, is preferably 18 or greater, more preferably 20 or greater, and even more preferably 21 or greater, with the upper limit being preferably 30 or less, more preferably 27 or less, and even more preferably 24 or less. If this value is too small, the spin rate on full shots will be high, and amateur users may not achieve the desired distance when hitting with a driver (W#1) or an iron, or the feel may be too hard. On the other hand, if this value is too large, the resilience will be low, and amateur users may not achieve the desired distance when hitting with a driver (W#1) or an iron, or the durability to cracking after repeated shots may be poor.

[0048] Regarding the core hardness distribution, it is preferable to optimize the value of (Cs-Cc) / (Cm-Cc). The value of (Cs-Cc) indicates the difference in hardness between the center and surface of the core, and the value of (Cm-Cc) indicates the difference in hardness between the midpoint between the core surface and the core center and the core center. The above formula represents the ratio of these hardness differences. The value of (Cs-Cc) / (Cm-Cc) is preferably 3.0 or greater, more preferably 3.5 or greater, and even more preferably 4.0 or greater. The upper limit is preferably 30.0 or less, more preferably 20.0 or less, and even more preferably 10.0 or less. If this value is too small, the spin rate on full shots will be high, and amateur users may not achieve the desired distance when hitting with a driver (W#1) or an iron. On the other hand, if this value is too large, the resilience will be low, preventing amateur users from achieving the desired distance when hitting with a driver (W#1) or an iron, and the durability to cracking during repeated shots may be poor.

[0049] In the above core hardness distribution, the following areas A to F ·Area A: 1 / 2×2×(Cm-4-Cm-6) ·Area B: 1 / 2×2×(Cm-2-Cm-4) ·Area C: 1 / 2×2×(Cm-Cm-2) ·Area D: 1 / 2×2×(Cm+2-Cm) ·Area E: 1 / 2×2×(Cm+4-Cm+2) ·Area F: 1 / 2×2×(Cm+6-Cm+4) Regarding the above, the value of (Area D + Area E) - (Area A + Area B) is preferably 4.0 or more, more preferably 4.5 or more, and even more preferably 5.0 or more, with the upper limit being preferably 15.0 or less, more preferably 10.0 or less, and even more preferably 8.0 or less. If this value is too small, the amount of spin on a full shot increases, and amateur users may not achieve the desired distance when hitting with a driver (W#1) or an iron. On the other hand, if this value is too large, the resilience decreases, and amateur users may not achieve the desired distance when hitting with a driver (W#1) or an iron, or the durability to cracking after repeated shots may be poor.

[0050] The value of (Area D + Area E) - (Area B + Area C) is preferably 3.5 or greater, more preferably 4.0 or greater, and even more preferably 4.5 or greater. The upper limit is preferably 15.0 or less, more preferably 10.0 or less, and even more preferably 7.0 or less. If this value is too small, the amount of spin on a full shot increases, and amateur users may not achieve the desired distance when hitting with a driver (W#1) or an iron. On the other hand, if this value is too large, the resilience decreases, and amateur users may not achieve the desired distance when hitting with a driver (W#1) or an iron, or the durability to cracking after repeated shots may be poor.

[0051] The value of {(Area D + Area E) - (Area A + Area B)} x (Cs - Cc) is preferably 80 or greater, more preferably 90 or greater, and even more preferably 110 or greater, with the upper limit being preferably 200 or less, more preferably 180 or less, and even more preferably 160 or less. The value of {(Area D + Area E) - (Area B + Area C)} x (Cs - Cc) is preferably 70 or greater, more preferably 80 or greater, and even more preferably 95 or greater, with the upper limit being preferably 200 or less, more preferably 180 or less, and even more preferably 140 or less. If these values ​​are too small, the spin rate on full shots increases, and amateur users may not achieve the desired distance when hitting with a driver (W#1) or with an iron. On the other hand, if these values ​​are too large, the resilience decreases, and amateur users may not achieve the desired distance when hitting with a driver (W#1) or with an iron, or the durability to cracking during repeated shots may be poor.

[0052] The relationship between the areas calculated from the hardness distribution is preferably Area E > Area C > Area A, more preferably (Area E + Area F) > Area D > Area C > Area A, and even more preferably (Area E + Area F) > Area D > (Area B + Area C) > Area A. If these relationships are not satisfied, the amount of spin will be high on full shots, and amateur users may not be able to achieve the desired distance when hitting with a driver (W#1) or an iron.

[0053] 2 is a schematic diagram illustrating areas A to F using the core hardness distribution data of Example 1. As such, areas A to F are the areas of triangles whose bases are the differences in specific distances and whose heights are the differences in hardness at each position.

[0054] Next, the envelope layer will be described. The surrounding layer may be formed of a single layer or multiple layers. When the surrounding layer is multiple layers, the total thickness of the surrounding layer corresponds to the thickness below, and the material hardness (sheet hardness) of the surrounding layer is the average hardness. When the surrounding layer is multiple layers, the surface hardness of the coated sphere in the outermost surrounding layer of the surrounding layer corresponds to the surface hardness below.

[0055] The material hardness of the envelope layer is not particularly limited, but is preferably 43 or more, more preferably 50 or more, and even more preferably 57 or more in Shore C hardness, with the upper limit being preferably 83 or less, more preferably 76 or less, and even more preferably 70 or less.The Shore D hardness is preferably 25 or more, more preferably 30 or more, and even more preferably 35 or more, with the upper limit being preferably 55 or less, more preferably 50 or less, and even more preferably 45 or less.

[0056] The surface hardness of an envelope-layer-coated sphere, which is a core coated with an envelope layer, is preferably 51 or more, more preferably 58 or more, and even more preferably 65 or more, in Shore C hardness, with an upper limit of preferably 91 or less, more preferably 84 or less, and even more preferably 78 or less.The Shore D hardness is preferably 31 or more, more preferably 36 or more, and even more preferably 41 or more, with an upper limit of preferably 61 or less, more preferably 56 or less, and even more preferably 51 or less.

[0057] If the material hardness and surface hardness of these envelope layers are too soft, the spin rate will be too high on full shots, and amateur users may not be able to achieve the desired distance when hitting with a driver (W#1) or an iron. Furthermore, the durability to cracking may be poor when hitting repeatedly. On the other hand, if the material hardness and surface hardness of the envelope layer are too hard, the impact feel will be too hard and the softness will be lost, and longest hitters may achieve excessive distance.

[0058] The thickness of the envelope layer is preferably 0.8 mm or more, more preferably 1.0 mm or more, and even more preferably 1.2 mm or more. The upper limit of the envelope layer thickness is preferably 1.5 mm or less, more preferably 1.4 mm or less, and even more preferably 1.3 mm or less. If the envelope layer is too thin, amateur users may not feel the soft feel when making full shots, or molding may become difficult, making mass production difficult. On the other hand, if the envelope layer is too thick, the resilience may decrease and the spin rate may increase, making it difficult for amateur users to achieve the desired distance when making full shots.

[0059] The material for the envelope layer is not particularly limited and may be any known resin material, specifically, ionomer resin or one or more thermoplastic elastomers selected from the group consisting of urethane, amide, ester, olefin, and styrene. In the present invention, ester-based thermoplastic elastomers, particularly thermoplastic polyether ester elastomers, are preferably used because they provide high resilience within the desired hardness range.

[0060] Next, the intermediate layer will be described. The material hardness of the intermediate layer is not particularly limited, but is preferably 71 or more, more preferably 78 or more, and even more preferably 84 or more in Shore C hardness, with the upper limit being preferably 95 or less, more preferably 92 or less, and even more preferably 90 or less.The Shore D hardness is preferably 46 or more, more preferably 50 or more, and even more preferably 53 or more, with the upper limit being preferably 61 or less, more preferably 60 or less, and even more preferably 59 or less.

[0061] The surface hardness of an intermediate layer-coated sphere, which is composed of a core coated with an envelope layer and an intermediate layer, is preferably 80 or more, more preferably 85 or more, and even more preferably 90 or more on the Shore C scale, with an upper limit of 96 or less, more preferably 95 or less, and even more preferably 94 or less.The surface hardness of an intermediate layer-coated sphere, which is composed of a core coated with an envelope layer and an intermediate layer, is preferably 80 or more, more preferably 85 or more, and even more preferably 90 or more on the Shore C scale, with an upper limit of 96 or less, more preferably 95 or less, and even more preferably 94 or less on the Shore D scale.The surface hardness of an intermediate layer-coated sphere is preferably 52 or more, more preferably 56 or more, and even more preferably 59 or more, with an upper limit of 67 or less, more preferably 65 or less, and even more preferably 63 or less on the Shore D scale.

[0062] If the material hardness and surface hardness of these intermediate layers are too soft, the spin rate will be too high on full shots, and amateur players may not be able to achieve the desired distance when hitting with a driver (W#1) or an iron. Furthermore, the launch angle on approaches will be low, making the ball difficult for amateur players to control. On the other hand, if the material hardness and surface hardness of the intermediate layer are too hard, the ball may feel too hard on impact, be less durable against cracking when hit repeatedly, or achieve excessive distance when hit by longest hitters.

[0063] The thickness of the intermediate layer is preferably 0.8 mm or more, more preferably 1.0 mm or more, and even more preferably 1.2 mm or more. The upper limit of the thickness of the intermediate layer is preferably 1.5 mm or less, more preferably 1.4 mm or less, and even more preferably 1.35 mm or less. If the intermediate layer is too thin, it may have poor crack resistance when repeatedly hit, or may be difficult to mold, making it unsuitable for mass production. On the other hand, if the intermediate layer is too thick, the feel on impact may be too hard, the resilience may be low, and amateur users may find it difficult to achieve good distances when hitting. Furthermore, if the thickness is outside the above range, the spin rate on full shots may increase, preventing amateur users from achieving good distances when hitting.

[0064] The intermediate layer is made of a resin material primarily containing an ionomer resin. Among ionomer resins, highly neutralized ionomers are particularly preferred. Commercially available highly neutralized ionomers are available, such as those under the trade names "HPF1000," "HPF2000," "HPF AD1035," and "HPF AD1040" (all manufactured by The Dow Chemical Company). The use of these highly neutralized ionomers reduces the spin rate of the ball on full shots while increasing the resilience of the ball, ensuring good distances for amateur players on full shots. To adjust the desired hardness of the intermediate layer material, the highly neutralized ionomers can be blended with other commonly used ionomers.

[0065] Next, the cover will be described. The cover material hardness is not particularly limited, but is preferably 83 or greater, more preferably 89 or greater, and even more preferably 93 or greater in Shore C hardness, with the upper limit being preferably 100 or less, more preferably 97 or less, and even more preferably 95 or less. The cover material hardness is preferably 55 or greater, more preferably 60 or greater, and even more preferably 63 or greater, with the upper limit being preferably 75 or less, more preferably 70 or less, and even more preferably 68 or less.

[0066] The surface hardness of a ball (entire sphere) including a core and a cover, in Shore C hardness, is preferably 90 or more, more preferably 93 or more, and even more preferably 95 or more, with the upper limit being preferably 100 or less, more preferably 99 or less, and even more preferably 98 or less. The Shore D hardness is preferably 62 or more, more preferably 67 or more, and even more preferably 69 or more, with the upper limit being preferably 76 or less, more preferably 74 or less, and even more preferably 72 or less.

[0067] If the cover's material hardness and surface hardness are too soft, the spin rate will be too high on full shots, and amateur players may not achieve the desired distance when hitting with a driver (W#1) or an iron. Furthermore, the launch angle on approaches will be low, making the ball difficult for amateur players to control. On the other hand, if the cover's material hardness and surface hardness are too hard, the feel on impact may be too hard, the durability against cracking after repeated shots may be poor, and longest hitters may achieve excessive distance.

[0068] The cover thickness is preferably 0.8 mm or more, more preferably 1.0 mm or more, and even more preferably 1.2 mm or more. The upper limit of the cover thickness is preferably 1.5 mm or less, more preferably 1.4 mm or less, and even more preferably 1.35 mm or less. If the cover is too thin, the crack resistance upon repeated impact may be poor, and cover molding may be difficult, resulting in poor mass productivity. On the other hand, if the cover is too thick, the feel on impact may be too hard and the resilience may be low, making it difficult for amateur users to achieve good distances when hitting the ball. Furthermore, if the thickness is outside the above range, the spin rate upon full shots may be high, preventing amateur users from achieving good distances when hitting the ball.

[0069] The cover is made of a resin material primarily composed of ionomer resin. When a urethane cover is used, the launch angle is lower during approach shots due to its inherent hardness, which can make it difficult for amateur golfers to handle. Even if the hardest grade of urethane is selected, the resilience is lower than that of an ionomer cover of the same hardness, preventing amateur golfers from achieving the desired distance. From the perspective of mass production, it is preferable to form the cover by injection molding an intermediate ball covered with the cover.

[0070] A resin material primarily made of ionomer resin is preferably used, with a preferred embodiment being a mixture of zinc-neutralized ionomer resin and sodium-neutralized ionomer resin used as the primary material. The blending ratio, zinc-neutralized / sodium-neutralized (by mass), is 5 / 95 to 95 / 5, preferably 20 / 80 to 90 / 10, and more preferably 25 / 75 to 75 / 25. If the zinc-neutralized ionomer and sodium-neutralized ionomer are not included within this ratio, the resilience may be too low to achieve the desired distance, and crack resistance may be poor during repeated impacts at room temperature, as well as at low temperatures (below freezing).

[0071] The cover material may contain various additives as needed, such as pigments, dispersants, antioxidants, light stabilizers, ultraviolet absorbers, and release agents.

[0072] A multi-piece solid golf ball formed by laminating the above-mentioned core, envelope, intermediate layer, and cover (outermost layer) can be manufactured by a conventional method, such as a known injection molding method. For example, the envelope layer material and intermediate layer material are sequentially injected into an injection mold around the core to obtain an envelope-layer-covered sphere and an intermediate layer-covered sphere, and finally, the cover material, which is the outermost layer, is injection molded to obtain a multi-piece golf ball. Alternatively, a golf ball can be manufactured by preparing two half-cups molded into a spherical half shell, encasing the core and intermediate layer-covered sphere in these, and then molding them under heat and pressure.

[0073] The golf ball preferably deflects 2.5 mm or more, more preferably 2.8 mm or more, and even more preferably 3.0 mm or more, when subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf). The upper limit of the deflection is preferably 3.8 mm or less, more preferably 3.5 mm or less, and even more preferably 3.3 mm or less. If the golf ball's deflection is too small, the spin rate on full shots may increase too much, resulting in amateur users losing distance when hitting with a driver (W#1) or with an iron, or the feel on impact may be too hard. On the other hand, if the deflection is too large, the initial velocity on impact may be too low, resulting in excessively short distances when longest hitters and amateur users hit with a driver (W#1), a soft feel on impact, or poor durability to cracking when hit repeatedly.

[0074] The initial velocity of the ball is preferably 75.0 m / s or greater, more preferably 76.5 m / s or greater, and even more preferably 77.0 m / s or greater, with the upper limit being 77.724 m / s or less. If this initial velocity value is too high, it will not comply with the official rules of the R&A and USGA. On the other hand, if this initial velocity is too low, the actual initial velocity will be low under all hitting conditions when making a full shot, and the desired flight distance may not be achieved. The initial velocity values ​​in this case are values ​​measured using a COR-type initial velocity meter, the same type as the R&A. Specifically, a COR-type initial velocity device manufactured by Hye Precision, USA, was used. The conditions for the measurement were as follows: the air pressure was changed to four levels, a relationship between the incident velocity and the COR was established, and the initial velocity at an incident velocity of 43.83 m / s was calculated from this relationship. The measurement environment for the COR-type initial velocity device is such that a ball that has been kept in a thermostatic chamber at 23.9±1°C for at least three hours is used, and measurements are taken at a room temperature of 23.9±2°C. The barrel diameter is selected so that the clearance between the outer diameter of the object being measured is between 0.2 and 2.0 mm on one side.

[0075] The value obtained by dividing the initial velocity of the ball by the deflection of the ball is preferably 19 or greater, more preferably 21 or greater, and even more preferably 23 or greater, with an upper limit of preferably 30 or less, more preferably 28 or less, and even more preferably 26 or less. This value is significant in measuring the initial velocity of the ball when it is actually hit. If this value is too high, the ball may travel too far when hit by a longest hitter, which may result in a failure to comply with the new Overall Distance Standard (ODS) rules. On the other hand, if this value is too low, the ball may spin too much on a full shot or the initial velocity may be low, making it impossible to achieve the desired distance under all hitting conditions.

[0076] The total thickness of the cover and intermediate layer is preferably 2.0 mm or more, more preferably 2.2 mm or more, and even more preferably 2.4 mm or more. The upper limit of this total thickness is preferably 3.8 mm or less, more preferably 3.0 mm or less, and even more preferably 2.7 mm or less. If this total thickness is too thin, the durability against cracking during repeated impacts may be poor, and molding the intermediate layer and cover may be difficult, resulting in poor mass production of the ball. On the other hand, if this total thickness is too thick, the feel may be too hard and the resilience may be low, making it difficult for amateur users to achieve good distances when hitting the ball. Furthermore, if the thickness is outside the above range, the spin rate on full shots may be high, preventing amateur users from achieving good distances when hitting the ball.

[0077] The total thickness of the cover, intermediate layer, and envelope layer is preferably at least 3.1 mm, more preferably at least 3.3 mm, and even more preferably at least 3.5 mm. The upper limit of this total thickness is preferably at most 5.0 mm, more preferably at most 4.2 mm, and even more preferably at most 3.9 mm. If the total thickness deviates from this range, the same adverse effects as those described above for the total thickness of the cover and intermediate layer may occur.

[0078] [Relationship between the surface hardness of each sphere] In the present invention, the relationship between the surface hardness of the ball, the envelope layer-covered sphere, and the intermediate layer-covered sphere is determined by the following formula (1-a) and the following formula (1-b): (Surface hardness of ball) > (Surface hardness of envelope-coated sphere) (1-a) (Surface hardness of ball) > (Surface hardness of intermediate layer-coated ball) (1-b) The relationship between the surface hardness of the core, the envelope layer-coated sphere, and the intermediate layer-coated sphere is expressed by the following formula (2-a) or (2-b): (Surface hardness of the envelope-coated sphere) < (Surface hardness of the core) (2-a) (Surface hardness of intermediate layer coated sphere) < (Surface hardness of core) (2-b) At least one of the following equations must be satisfied. Note that the hardness in the above equations refers to Shore C hardness. If the surface hardness of the ball is less than that of the inner layer, the launch angle when an amateur user approaches may be low, making the ball difficult for amateur users to hit. Furthermore, the softer of the surface hardness of the intermediate layer-covered ball and the surface hardness of the envelope layer-covered ball must be lower than the surface hardness of the core. If this hardness relationship is not satisfied, it may be difficult to achieve both a soft feel on full shots and a bouncy, long-distance feel.

[0079] A more preferred embodiment of the above hardness relationship is one that satisfies the following formula: (Surface hardness of ball) > (Surface hardness of intermediate layer coated ball) > (Surface hardness of envelope layer coated ball) If this hardness relationship is not satisfied, it may not be possible for amateur users to achieve both ease of lift when approaching the ball, a good feel on impact, and good durability against repeated impacts.

[0080] The most suitable hardness relationship in the present invention is expressed by the following formula: (Surface hardness of ball) > (Surface hardness of mid-layer coated ball) > (Surface hardness of envelope coated ball) < (Surface hardness of core) The purpose is to satisfy the following.

[0081] The surface hardness of the ball minus the surface hardness of the intermediate layer-coated sphere is preferably greater than 0, more preferably greater than 2, and even more preferably greater than 4, in Shore C hardness, with an upper limit of preferably 25 or less, more preferably 15 or less, and even more preferably 10 or less. If this value is too low, the amount of spin on a full shot increases, preventing amateur users from achieving the desired distance when hitting a full shot with a driver (W#1) or iron, or the launch angle on an approach shot may be too low, making the approach shot feel difficult for amateur users. If this value is too high, the club may be less durable to cracking after repeated impacts, or the initial velocity may be low, resulting in shorter-than-desired distances on all driver (W#1) shots.

[0082] The surface hardness of the intermediate layer-coated ball minus the surface hardness of the envelope layer-coated ball is preferably greater than 0, more preferably at least 10, and even more preferably at least 20, with an upper limit of preferably no greater than 40, more preferably no greater than 32, and even more preferably no greater than 25. If this value is too large, the club may have poor crack resistance when repeatedly hit, or may have high spin rates and low initial velocities on full shots, resulting in shorter than desired distances on all driver (W#1) shots.

[0083] The value obtained by subtracting the surface hardness of the envelope-coated sphere from the surface hardness of the core is preferably greater than 0, preferably at least 2, more preferably at least 4, with an upper limit of preferably at most 12, more preferably at most 9, and even more preferably at most 6. The value obtained by subtracting the center hardness of the core from the surface hardness of the envelope-coated sphere, in Shore C hardness, is preferably at least 8, more preferably at least 12, and even more preferably at least 15, with an upper limit of preferably at most 30, more preferably at most 25, and even more preferably at most 20. If these values ​​are too large, the feel of the ball may not be soft on full shots. On the other hand, if these values ​​are too small, the amount of spin on full shots increases, and amateur users may not achieve the desired distance on full shots with a driver (W#1) or iron.

[0084] The value obtained by subtracting the surface hardness of the core from the surface hardness of the ball, in Shore C hardness, is preferably 10 or more, more preferably 13 or more, and even more preferably 18 or more, with the upper limit being preferably 35 or less, more preferably 30 or less, and even more preferably 25 or less. The value obtained by subtracting the center hardness of the core from the surface hardness of the ball, in Shore C hardness, is preferably 30 or more, more preferably 35 or more, and even more preferably 40 or more, with the upper limit being preferably 55 or less, more preferably 50 or less, and even more preferably 45 or less. If these values ​​are too large, the club may have poor crack resistance when repeatedly hit, or the initial velocity may be low, resulting in shorter than desired distances for all driver (W#1) shots. On the other hand, if these values ​​are too small, the spin rate on full shots may be high, preventing amateur players from achieving the desired distances for driver (W#1) shots and iron shots.

[0085] [Relationship between the core and the amount of ball deflection] When the core and ball are subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf), the deflection (mm) is defined as C (mm) and B (mm), respectively. The value of C / B is preferably 1.00 mm or more, more preferably 1.20 mm or more, and even more preferably 1.40 mm or more, with an upper limit of preferably 2.00 mm or less, more preferably 1.80 mm or less, and even more preferably 1.60 mm or less. The C / B value is also preferably 1.20 or more, more preferably 1.30 or more, and even more preferably 1.40 or more, with an upper limit of preferably 1.60 or less, more preferably 1.55 or less, and even more preferably 1.50 or less. If these values ​​are too large, the durability to cracking during repeated impacts may be poor, the initial velocity may be low, and the distance traveled by all driver (W#1) shots may be shorter than desired. Alternatively, the ball may not feel centered on full shots, resulting in a lack of distance. On the other hand, if these values ​​are too small, the amount of spin will be too great when hitting a full shot, and amateur users may not be able to achieve the desired distance when hitting with a driver (W#1) or an iron, or may not feel a soft impact.

[0086] [About core diameter and ball diameter] The relationship between the core diameter and the ball diameter, i.e., the ratio (core diameter) / (ball diameter), is preferably 0.766 or greater, more preferably 0.803 or greater, and even more preferably 0.817 or greater. The upper limit is preferably 0.855 or less, more preferably 0.845 or less, and even more preferably 0.836 or less. If this ratio is too small, the initial velocity of the ball will be low, or the overall deflection of the ball will be small, making the ball harder. This may increase the spin rate of the ball on full shots, preventing amateur players from achieving the desired distance on full shots. On the other hand, if this ratio is too large, the spin rate of the ball will be high, preventing amateur players from achieving the desired distance on full shots, or may result in poor durability to cracking after repeated impacts.

[0087] A large number of dimples can be formed on the outer surface of the cover. There are no particular limitations on the number of dimples arranged on the cover surface, but the number is preferably 280 or more, more preferably 300 or more, and more preferably 310 or more, with the upper limit being preferably 450 or less, more preferably 400 or less, and even more preferably 350 or less. If the number of dimples deviates from the above range, amateur users may experience reduced flight distance when hitting with a driver (W#1).

[0088] The dimples may be of one or a combination of two or more shapes, such as circular, polygonal, dewdrop, or elliptical. For example, if circular dimples are used, the diameter may be approximately 2.5 mm to 6.5 mm, and the depth may be 0.08 mm to 0.30 mm.

[0089] The dimple coverage of the golf ball's spherical surface, specifically the ratio of the total dimple area defined by the flat surface edges surrounded by the edges of the dimples to the ball's area assuming no dimples (SR value), is preferably at least 75%, more preferably at least 80%, and even more preferably at least 84%, with an upper limit of 90%, more preferably at most 88%, and even more preferably at most 86%. If the SR value falls outside this range, amateur users may experience reduced flight distance when hitting with a driver (W#1).

[0090] The VR value, which is the percentage of the total dimple volume below the plane surrounded by the dimple edges relative to the ball volume assuming no dimples exist, is 0.75% or greater, preferably 0.78% or greater, and more preferably 0.80% or greater, with an upper limit of 0.89%, more preferably 0.88%, and even more preferably 0.86%. If this VR value is greater than the above range, longest hitters may experience a significant decrease in distance when hitting with a driver (W#1), or amateur players may not achieve the desired distance when hitting with a driver (W#1). This may also result in a lower trajectory, making it difficult to achieve carry and making it difficult to clear valleys or ponds. On the other hand, if this value is too small, longest hitters may experience a similar decrease in distance when hitting with a driver (W#1), resulting in a ball flying farther than the upper limit of the new Overall Standard Distance (ODS) rule.

[0091] The total volume of dimples refers to the sum of the volumes of all dimples formed on a single ball, which are formed below the plane surrounded by the edges of the dimples. There are no particular restrictions on the total volume of dimples, but it is preferably 306 mm 3 More than 318mm, preferably 318mm 3 , and more preferably 326 mm 3 The upper limit is preferably 363 mm. 3 Less than or equal to 359mm, preferably 3 Less than or equal to 351 mm, more preferably 3 The total dimple volume is as follows. If the total dimple volume value is greater than the above range, the distance traveled by longest hitters with a driver (W#1) may be too short, or amateur users may not achieve the desired distance when hitting with a driver (W#1). This may also result in a lower trajectory, making it difficult to achieve carry and making it difficult to clear valleys or ponds. On the other hand, if the above value is too small, the distance traveled by longest hitters with a driver (W#1) may not be reduced, and the ball may fly beyond the upper limit of the new Overall Standard Distance (ODS) rule.

[0092] The value V0, calculated by dividing the void volume of the dimple below the plane surrounded by the edge of each dimple by the volume of a cylinder whose base is the plane and whose height is the maximum depth of the dimple from the bottom, is preferably at least 0.35, more preferably at least 0.38, and even more preferably at least 0.40, with an upper limit of 0.80, more preferably at most 0.70, and even more preferably at most 0.60. If this V0 value falls outside the above range, longest hitters and amateur players may experience shorter flight distances than desired when hitting with a driver (W#1).

[0093] For the golf ball of the present invention, when the ratio (CL1 / CD1) of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm is A1, the ratio (CL2 / CD2) of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm is A2, and the ratio (CL3 / CD3) of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm is A3, the following two equations can be used to determine the ratio: 0.590≦A1≦0.655, and (A2+A3) / 2≧0.670 The dimples are appropriately designed to satisfy the above.

[0094] In this specification, "lift coefficients (CL1, CL2, CL3) and drag coefficients (CD1, CD2, CD3)" are measured in accordance with the ITR (Indoor Test Range) established by the USGA (United States Golf Association). The lift coefficient and drag coefficient can be adjusted by adjusting the configuration of the dimples on the golf ball (arrangement, diameter, depth, volume, number, shape, etc.). The lift coefficient and drag coefficient are independent of the internal configuration of the golf ball. The Reynolds number (Re) is a dimensionless number used in the field of fluid dynamics. The Reynolds number (Re) is calculated using the following equation (1): Re = ρvL / μ (1) In the above equation (1), ρ represents the density of the fluid, v represents the average velocity of the object relative to the fluid flow, L represents the characteristic length, and μ represents the viscosity coefficient of the fluid.

[0095] In the present invention, the ratio CL1 / CD1 of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm is defined as A1, the ratio CL2 / CD2 of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm is defined as A2, and the ratio CL3 / CD3 of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm is defined as A3.

[0096] Regarding the conditions under which the lift coefficient CL1 and drag coefficient CD1 are measured, namely a Reynolds number of 218,000 and a spin rate of 2,800 rpm, these high-speed conditions correspond to the conditions under which a longest hitter hits the ball with a driver (W#1), and this Reynolds number corresponds to the ball speed when a golf ball is hit at a head speed (HS) of 54 m / s, and a spin rate of 2,800 rpm is the average spin condition for a player with a head speed (HS) of 54 m / s.

[0097] Regarding the conditions for measuring the lift coefficient CL2 and drag coefficient CD2, namely a Reynolds number of 184,000 and a spin rate of 2,900 rpm, these medium speed conditions correspond to the conditions when an amateur user hits the ball with a driver (W#1) at a head speed (HS) of 45 m / s. This Reynolds number corresponds to the ball speed when a golf ball is hit at a head speed (HS) of 45 m / s, and a spin rate of 2,900 rpm is the average spin condition for a player with a head speed (HS) of 45 m / s.

[0098] Regarding the conditions for measuring the lift coefficient CL3 and drag coefficient CD3, namely a Reynolds number of 158,000 and a spin rate of 3,100 rpm, these low-speed conditions correspond to the conditions when an amateur user hits the ball with a driver (W#1) at a head speed (HS) of 40 m / s. This Reynolds number corresponds to the ball speed when a golf ball is hit at a head speed (HS) of 40 m / s, and a spin rate of 3,100 rpm is the average spin condition for a player with a head speed (HS) of 40 m / s.

[0099] The ratio of the lift coefficient CL1 to the drag coefficient CD1, i.e., the value of CL1 / CD1=A1, is 0.590 or greater, preferably 0.595 or greater, more preferably 0.600 or greater, with an upper limit of 0.655 or less, preferably 0.640 or less, more preferably 0.627 or less. If this value is too large, the distance traveled by a longest hitter using a driver (W#1) may not decrease, resulting in a ball flying farther than the upper limit of the new overall standard distance (ODS) rule. On the other hand, if this value is too small, the ball may fly too far below the target distance under all hitting conditions.

[0100] When the value of A1 is 0.590 to 0.613, the ratio of the lift coefficient CL2 to the drag coefficient CD2 (i.e., the value of CL2 / CD2 = A2) is preferably 0.635 or greater, more preferably 0.645 or greater, and even more preferably 0.655 or greater, with the upper limit being preferably 0.668 or less, more preferably 0.666 or less, and even more preferably 0.664 or less. Furthermore, when the value of A1 is 0.614 to 0.655, the value of A2 is preferably 0.669 or greater, more preferably 0.671 or greater, and even more preferably 0.673 or greater, with the upper limit being preferably 0.750 or less, more preferably 0.725 or less, and even more preferably 0.700 or less. If the values ​​fall outside the above ranges, the ball may fly high or lose its extension under all hitting conditions, resulting in a trajectory with little carry and preventing the desired total distance from being achieved.

[0101] When the value of A1 is 0.590 to 0.613, the ratio of the lift coefficient CL3 to the drag coefficient CD3 (i.e., the value of CL3 / CD3 = A3) is preferably 0.695 or greater, more preferably 0.705 or greater, and even more preferably 0.715 or greater, with the upper limit being preferably 0.734 or less, more preferably 0.731 or less, and even more preferably 0.728 or less. Furthermore, when the value of A1 is 0.614 to 0.655, the value of A3 is preferably 0.735 or greater, more preferably 0.738 or greater, and even more preferably 0.741 or greater, with the upper limit being preferably 0.815 or less, more preferably 0.780 or less, and even more preferably 0.760 or less. If the values ​​fall outside the above ranges, the ball may fly up or lose its extension under all hitting conditions, resulting in a trajectory with little carry and preventing the desired total distance from being achieved.

[0102] The average of the above A2 and A3 values, i.e., the value of (A2 + A3) / 2, is 0.670 or more, preferably 0.680 or more, more preferably 0.690 or more, with the upper limit being preferably 0.783 or less, more preferably 0.775 or less, and even more preferably 0.765 or less. If this value is too low, amateur users may not achieve the desired total distance when hitting with a driver (W#1) without achieving carry. On the other hand, if this value is too high, amateur users may not achieve the desired total distance when hitting with a driver (W#1) without achieving the desired trajectory.

[0103] The total volume of the dimples is D (mm 3), and the deflection when the ball is subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf) is B (mm), the D / B value is preferably 140 or less, more preferably 130 or less, and even more preferably 120 or less. On the other hand, the lower limit is preferably 95 or more, more preferably 97 or more, and even more preferably 100 or more. This D / B is an index that provides an appropriate distance control effect when hit with a driver (W#1) by longest hitters and facilitates good distance when hit by amateur users. If this value falls outside the above range, longest hitters and amateur users may not be able to achieve the desired distance when hit with a driver (W#1).

[0104] The golf ball of the present invention can be made to conform to the Rules of Golf for competitive use, with an outer diameter that does not pass through a ring with an inner diameter of 42.672 mm, and a mass preferably ranging from 45.0 to 45.93 g. [Example]

[0105] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0106] [Examples 1 to 4, Comparative Examples 1 to 15] Core formation For Comparative Examples 8, 10, and 12 to 14, the rubber compositions of each example shown in Table 1 were prepared, and then vulcanized and molded under the vulcanization conditions of each example shown in Table 1 to produce solid cores.

[0107] For Examples 1 to 4 and Comparative Examples 1 to 7, 9, 11, and 15, cores were prepared based on the formulations in Table 1 in the same manner as above.

[0108] [Table 1]

[0109] Details of the above formulation are as follows: Polybutadiene A: Product name "BR01" (manufactured by ENEOS Materials Co., Ltd.) Polybutadiene B: Product name "Diene 645" (Firestone Polymers) Polybutadiene C: Product name "BUDENE 1224G" (Goodyear Tire & Rubber Company) Isoprene rubber: Product name "IR2200" (manufactured by ENEOS Materials Co., Ltd.) Styrene-butadiene rubber: Product name "SBR1507" (manufactured by ENEOS Materials Co., Ltd.) Zinc acrylate: Product name "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.) Zinc methacrylate: Trade name "ZDA-90" (manufactured by Asada Chemical Industry Co., Ltd.) Zinc stearate: Product name "BR-3T" (manufactured by Akrochem) Organic peroxide A: Dicumyl peroxide, trade name "Percumyl D" (manufactured by NOF Corporation) Organic peroxide B: a mixture of 1,1-di(t-butylperoxy)cyclohexane and silica, trade name "Perhexa C-40" (manufactured by NOF Corporation) Sulfur: Product name: "Sunmix S-80N" (manufactured by Sanshin Chemical Industry Co., Ltd., containing 80 wt% powdered sulfur for rubber) Water: Pure water (Seiki Pharmaceutical Co., Ltd.) Antioxidant: 2,2-methylenebis(4-methyl-6-butylphenol), product name "Nocrac NS-6" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Zinc oxide: Product name "Triple Zinc Oxide" (manufactured by Sakai Chemical Industry Co., Ltd.) Pentachlorothiophenol zinc salt: Fujifilm Wako Pure Chemical Industries, Ltd.

[0110] Formation of the envelope layer, intermediate layer and cover (outermost layer) Next, for Comparative Examples 8, 10, and 12 to 14, an intermediate layer was formed by injection molding the intermediate layer resin material No. 4 or No. 5 shown in Table 2 around the surface of the core using an injection mold. Next, a cover (outermost layer) resin material No. 10 shown in Table 2 was injection molded around the intermediate layer-covered sphere using another injection mold to form a cover. During this process, a large number of predetermined dimples, as described below, were formed on the surface of the cover.

[0111] For Examples 1 to 4 and Comparative Examples 1 to 3, an injection mold was used to injection mold the envelope layer resin material No. 1 shown in Table 2 around the core surface to form the envelope layer. Then, another injection mold was used to injection mold the envelope layer resin material No. 2 shown in the same table around the envelope layer-coated sphere to form the envelope layer. Then, another injection mold was used to injection mold the cover (outermost layer) resin material No. 6 shown in the same table around the envelope layer-coated sphere to form the cover. For Comparative Examples 4, 5, 9, and 11, an injection mold was used to injection mold the envelope layer around the core surface with the resin material No. 2, No. 3, or No. 4 shown in Table 2, and then the cover was injection molded with the cover (outermost layer) resin material No. 7 to No. 10 shown in the same table to form the cover. For Comparative Examples 6, 7, and 15, a cover was formed by injection molding around the core surface using resin material No. 8, No. 9, or No. 11 shown in Table 2. At this time, a large number of predetermined dimples, as described below, were formed on the cover surface.

[0112] [Table 2]

[0113] The details of the ingredients in Table 2 are as follows: "Hytrel 4047N" polyester elastomer manufactured by Toray Celanese "HPF1000" Highly neutralized ionomer manufactured by The Dow Chemical Company "Himilan 1605," "Himilan 1601," "Himilan 1557," "Himilan 1706," "AM7329," "AM7327," and "AM7318" are ionomers manufactured by Mitsui Dow Polychemicals. "AN4319" Nucrel manufactured by Mitsui Dow Polychemicals "Barium sulfate": Product name "Precipitated Barium Sulfate 300" manufactured by Sakai Chemical Industry Co., Ltd. "Magnesium stearate" is a product name of Nissin Corporation's "Magnesium Stearate G" "Trimethylolpropane" (TMP) manufactured by Tokyo Chemical Industry Co., Ltd. "TPU (1)" is a product name "Pandex" manufactured by DIC Covestro Polymers, an ether-type thermoplastic polyurethane with a material hardness (Shore D) of 50. "TPU (2)" is a product name "Pandex" manufactured by DIC Covestro Polymers, an ether-type thermoplastic polyurethane with a Shore D hardness of 47.

[0114] The dimples used in each example and comparative example were dimples (1) to (5) shown below. Each dimple pattern included eight types of circular dimples, No. 1 to No. 8, with different diameters and depths. Details are shown in Table 3 below. The arrangement (pattern) of dimples (1) to (5) is shown in Figure 5. Figure 5(A) shows a plan view of the dimples, and Figure 5(B) is a side view.

[0115] [Table 3]

[0116] Dimple definition Edge: The highest point on the cross section passing through the center of the dimple Diameter: The diameter of the plane enclosed by the dimple edge Depth: The maximum depth of the dimple from the plane bounded by the dimple edge SR: The ratio of the total dimple area, defined as the plane surrounded by the edges of the dimples, to the area of ​​the ball as if no dimples existed. Dimple volume: The volume of the dimple below the plane surrounded by the dimple edge Cylinder volume ratio: The ratio of the dimple volume to the volume of a cylinder with the same diameter and depth as the dimple. VR: The total volume of the dimples formed below the plane surrounded by the edges of the dimples is the volume of the ball as if no dimples existed.

[0117] The following table shows the lift coefficient CL1, drag coefficient CD1, and ratio CL1 / CD1=A1 for a ball with a Reynolds number of 218,000 and a spin rate of 2,800 rpm; the lift coefficient CL2, drag coefficient CD2, and ratio CL2 / CD2=A2 for a Reynolds number of 184,000 and a spin rate of 2,900 rpm; and the lift coefficient CL3, drag coefficient CD3, and ratio CL3 / CD3=A3 for a Reynolds number of 158,000 and a spin rate of 3,100 rpm for a ball with the above dimples (1) to (5) formed on the cover surface. These lift and drag coefficients were measured in accordance with the ITR (Indoor Test Range) established by the USGA.

[0118] [Table 4]

[0119] For each of the resulting golf balls, various physical properties such as the internal hardness at each position of the core, the outer diameter of the core and each coated sphere, the thickness and material hardness of each layer, the surface hardness of each coated sphere, and the initial velocity of the ball were evaluated using the methods described below, and the results are shown in Tables 5 to 8.

[0120] Core hardness distribution The core's surface is spherical, and the needle of a hardness tester is set nearly perpendicular to the spherical surface, and the surface hardness is measured in Shore C hardness in accordance with ASTM D2240. For the center and designated locations of the core, the core is cut into a hemisphere, the cross section is flattened, and the needle of the hardness tester is pressed perpendicularly against the center and the designated locations shown in Tables 5 and 6. The hardness at the center and each location is shown in Shore C hardness. Hardness measurements are performed using an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd., equipped with a Shore C hardness tester. The maximum hardness value is read. All measurements are performed in an environment of 23±2°C. The values ​​in the table are Shore C hardness values. In addition, the core hardness distribution is calculated by dividing the Shore C hardness Cc at the center of the core by the Shore C hardness C at the midpoint M between the center and the surface of the core. m The Shore C hardness Cm-2, Cm-4, Cm-6 at positions 2mm, 4mm, and 6mm inward from the midpoint M, the Shore C hardness Cm+2, Cm+4, Cm+6 at positions 2mm, 4mm, and 6mm outward from the midpoint M, and the Shore C hardness Cs on the core surface are as follows: Areas A to F ·Area A: 1 / 2×2×(Cm-4-Cm-6) ·Area B: 1 / 2×2×(Cm-2-Cm-4) ·Area C: 1 / 2×2×(Cm-Cm-2) ·Area D: 1 / 2×2×(Cm+2-Cm) ·Area E: 1 / 2×2×(Cm+4-Cm+2) ·Area F: 1 / 2×2×(Cm+6-Cm+4) Calculate the values ​​of the following nine formulas. (1)Area A+Area B (2)Area B+Area C (3)Area C+Area D (4)Area D+Area E (5)Area E+Area F (6)(Area D+Area E)-(Area A+Area B) (7)(Area D+Area E)-(Area B+Area C) (8){(Area D+Area E)-(Area A+Area B)}×(Cs-Cc) (9){(Area D+Area E)-(Area B+Area C)}×(Cs-Cc)

[0121] To explain the areas A to F of the core hardness distribution, a schematic diagram showing the areas A to F using the core hardness distribution data of Example 1 is shown in FIG. Graphs of the core hardness distributions of Examples 1 to 4 and Comparative Examples 1 to 15 are shown in FIGS.

[0122] The outer diameter of each of the core, the envelope layer-coated sphere, and the intermediate layer-coated sphere The temperature is adjusted to 23.9±1°C in a thermostatic chamber for at least 3 hours, and then measurements are taken at any 5 points on the surface in a room at 23.9±2°C. The average value is used as the measurement value for one sphere, and the average value for 10 measurements is calculated.

[0123] Ball diameter The ball is placed in a thermostatic chamber at 23.9±1°C for at least three hours, and then 15 randomly selected non-dimpled areas are measured in a room at 23.9±2°C. The average of these measurements is used as the measurement value for one ball, and the average value for 10 balls is calculated.

[0124] Deflection of the core and ball Each core or ball is placed on a hard plate and the deflection is measured when an initial load of 98N (10kgf) is applied and a final load of 1275N (130kgf) is applied. The deflection is measured in a room at 23.9±2°C after being regulated at 23.9±1°C for at least three hours. A high-load compression tester manufactured by MU Seiki Co., Ltd. is used as the measuring device, and the down speed of the pressure head compressing the core or ball is 10mm / s.

[0125] Material hardness of the envelope layer, mid layer, and cover (Shore C hardness, Shore D hardness) The resin material for each layer is formed into a 2mm thick sheet and left to stand for two weeks at a temperature of 23±2°C. Three sheets are stacked together during measurement. The Shore C hardness and Shore D hardness are measured using a Shore C hardness tester and a Shore D hardness tester, respectively, that conform to the ASTM D2240 standard. To measure hardness, an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd., equipped with a Shore C or Shore D hardness tester, is used. The hardness value is read as the maximum value. The measurement method follows the ASTM D2240 standard.

[0126] Surface hardness of the envelope layer coated sphere, the intermediate layer coated sphere, and the ball Measurements are taken by pressing a needle perpendicularly against the surface of each sphere. The surface hardness of the ball (cover) is measured on the land area on the ball surface where no dimples are formed. Shore C hardness and Shore D hardness are measured using a Shore C hardness tester and a Shore D hardness tester, respectively, that comply with the ASTM D2240 standard. To measure hardness, an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd., equipped with a Shore C or Shore D hardness tester, is used. The hardness value is read as the maximum value. The measurement method complies with the ASTM D2240 standard.

[0127] Initial velocity of the ball The initial velocity of each ball is measured at 23.9±2°C using a COR type initial velocity meter manufactured by Hye Precision Products, the same type as that used by the R&A. The measurement principle is as follows. The air pressure is changed to four levels: 35.5, 36.5, 39.5, and 40.5 psi. The ball is launched at four different entry velocities at each air pressure, and the ball is allowed to collide with the barrier, measuring its COR (coefficient of restitution). In other words, the air pressure is changed to four levels, and a correlation equation is created between entry velocity and COR. Similarly, a correlation equation is created between entry velocity and contact time. Then, from these correlation equations, the COR (coefficient of restitution) and contact time (μs) at an incident velocity of 43.83 m / s are calculated, and substituted into the initial velocity conversion formula below to calculate the initial velocity of each ball. IV=136.8+136.3e+0.019tc (Where e is the coefficient of restitution and tc is the contact time (μs) at an impact velocity of 143.8 ft / s (43.83 m / s).) For all ball initial velocity measurements, a barrel diameter of 43.18 mm is selected.

[0128] [Table 5]

[0129] [Table 6]

[0130] [Table 7]

[0131] [Table 8]

[0132] The distance (W#1) and controllability on approach of each golf ball were evaluated by the following methods. The results are shown in Table 9.

[0133] Distance rating (W#1, HS54m / s) A driver club is attached to the golf hitting robot, and the spin rate and total distance are measured when hitting the ball at a head speed (HS) of 54 m / s. The club used is the Bridgestone Sports TourB XD-5 Driver (2017 model) (loft angle 8.5°), and evaluation is based on the following criteria. 〔Judgment criteria〕 ◯: The total compared to Comparative Example 10 is −10 m or less and −14 m or more. △ The total compared to Comparative Example 10 is less than -14 m. × The total compared to Comparative Example 10 is greater than -10m.

[0134] Distance rating (W#1, HS40m / s) A driver club is attached to the golf hitting robot, and the spin rate and total distance are measured when hitting the ball at a head speed (HS) of 40 m / s. The club used is the Bridgestone Sports J015 Driver (2016 model) (loft angle 9.5°), and evaluation is based on the following criteria. 〔Judgment criteria〕 ◯: The total compared to Comparative Example 10 is 0 m or more. △: The total compared to Comparative Example 10 is equal to or greater than -5 m and less than 0 m. × The total compared to Comparative Example 10 is less than −5 m.

[0135] Distance rating (I#6, HS42m / s) A 6-iron (I#6) was attached to the golf hitting robot and hit at a head speed (HS) of 42 m / s, and the spin rate and total distance were measured. The club used was the Bridgestone Sports JGR Forged I#6 (2016 model), and was evaluated according to the following criteria. 〔Judgment criteria〕 ◯: The total compared to Comparative Example 10 is 5 m or more. △: The total compared to Comparative Example 10 is 0 m or more and less than 5 m. × The total compared to Comparative Example 10 is less than 0 m.

[0136] Distance rating (I#6, HS35m / s) A 6-iron (I#6) was attached to the golf hitting robot and hit at a head speed (HS) of 35 m / s, and the spin rate and total distance were measured. The club used was the Bridgestone Sports JGR Forged I#6 (2016 model), and was evaluated according to the following criteria. [Judgment criteria / total] ◯: The total compared to Comparative Example 10 is 3 m or more. △: The total compared to Comparative Example 10 is equal to or greater than -3 m and less than 3 m. × The total compared to Comparative Example 10 is less than −3 m.

[0137] Evaluation of launch angle during approach The evaluation was based on the launch angle when a sand wedge was attached to a golf hitting robot and hit at a head speed (HS) of 15 m / s. The launch angle was measured using an initial condition measuring device on the ball immediately after hitting. The sand wedge used was the "TourStage TW-03 (loft angle 57°) 2002 model" manufactured by Bridgestone Sports. 〔Judgment criteria〕 ○ Launch angle is 35.0° or more × Launch angle is less than 35.0°

[0138] Evaluation of feel A sensory evaluation of the hitting feel was carried out by amateur golfers with a handicap of 25 or more and a driver (W#1) head speed of 30-40 m / s. Evaluation was based on the following criteria. 〔Judgment criteria〕 ○ ··· It has a good feel with a soft and bouncy feel. △ Neither the softness nor the bounce feel is particularly good. × Neither the softness nor the resilience is particularly good. Or, either the softness or the resilience is clearly not good.

[0139] [Table 9]

[0140] As shown in the results in Table 9, the golf balls of Comparative Examples 1 to 15 are inferior to the products of the present invention (Examples) in the following respects. In Comparative Example 1, the dimple VR was less than 0.75% and A1 was greater than 0.655. The initial ball velocity was lower than 75.0 m / s. Furthermore, the total dimple volume D (mm 3) divided by the deflection B (mm) when the ball is loaded with 10-130 kgf (hereinafter referred to as the "D / B value") is less than 95. As a result, the distance when hit with a driver (W#1) at a head speed (HS) of 40 m / s is short, and the distance when hit with a 6-iron (I#6) is also short. In addition, the feel of the club is clearly insufficient. In Comparative Example 2, the dimple VR was less than 0.75% and the A1 was greater than 0.655. The D / B value was also less than 95. As a result, the flight distance when hit with a driver (W#1) at a head speed (HS) of 54 m / s was long, which does not comply with the new ODS rules. In Comparative Example 3, the dimple VR was greater than 0.89%, A1 was less than 0.590, and (A2 + A3) / 2 was less than 0.670. As a result, the ball was poor in distance when hit with a driver (W#1) at both a head speed (HS) of 54 m / s and a head speed (HS) of 40 m / s. Comparative Example 4 is a golf ball with a three-piece structure without an envelope layer, in which the surface hardness of the intermediate layer-covered sphere is greater than the surface hardness of the core, resulting in a softer feel when hit than the examples. Comparative Example 5 is a golf ball with a three-piece structure without an envelope layer, in which the surface hardness of the intermediate layer-covered sphere is greater than the surface hardness of the core, resulting in a softer feel when hit than the examples. Comparative Example 6 is a golf ball having a two-piece structure consisting of only a core and a cover. As a result, the feel on impact was inferior to that of each of the Examples in terms of softness. Comparative Example 7 is a golf ball with a two-piece structure consisting of only a core and a cover. The D / B value is less than 95. As a result, the flight distance when hit with a driver (W#1) at a head speed (HS) of 54 m / s is too short, and the flight distance when hit with a driver (W#1) at a head speed (HS) of 40 m / s is slightly shorter, and the resilience is insufficient. Comparative Example 8 had a three-piece structure in which the surface hardness of the ball was softer than that of the intermediate layer-covered ball. The D / B value was greater than 140, and the surface hardness of the intermediate layer-covered ball was harder than that of the core. As a result, the ball had a short distance when hit with an iron (I#6), and the launch angle on approach shots was too low, making it difficult for amateurs to hit. The ball also had a poor feel. Comparative Example 9 has a three-piece structure in which the surface hardness of the ball is softer than that of the intermediate layer-covered ball. The D / B value is greater than 140, and the surface hardness of the intermediate layer-covered ball is greater than that of the core. As a result, the ball's flight distance when hit with a driver (W#1) at a head speed (HS) of 54 m / s is long, which does not comply with the new ODS rules. Furthermore, the ball's flight distance when hit with an iron (I#6) is short, and the launch angle on approach shots is too low, making it difficult for amateurs to hit. Furthermore, the ball's soft feel is poor. Comparative Example 10 is one of the embodiments currently used by male professional golfers. The ball had a three-piece structure with a surface hardness lower than that of the mid-layer-covered ball. The dimple VR was less than 0.75% and the A1 was greater than 0.655. Furthermore, the surface hardness of the mid-layer-covered ball was greater than that of the core. As a result, the ball achieved a long distance when hit with a driver (W#1) at a head speed (HS) of 54 m / s, failing to comply with the new ODS rules. Furthermore, the ball achieved poor distance when hit with a driver (W#1) at a HS of 40 m / s and when hit with an iron (I#6). The launch angle on approach shots was too low, making the ball difficult for amateurs to hit. Furthermore, the ball had a poor soft feel. Comparative Example 11 had a three-piece structure in which the surface hardness of the ball was softer than that of the intermediate layer-covered ball. The dimple VR was greater than 0.89%, A1 was less than 0.590, and (A2 + A3) / 2 was less than 0.670. Furthermore, the D / B value was greater than 140, meaning the surface hardness of the intermediate layer-covered ball was harder than that of the core. As a result, the ball's flight distance was significantly reduced when hit with a driver (W#1) at a head speed (HS) of 54 m / s, and the ball's flight distance was also poor when hit with both a driver (W#1) at a head speed (HS) of 40 m / s and an iron (I#6) at a head speed (HS) of 42 m / s. Furthermore, the launch angle on approach shots was too low, making the ball difficult for amateurs to hit, and the ball also had a poor feel. Comparative Example 12 had a three-piece structure in which the surface hardness of the ball was softer than that of the intermediate layer-covered ball. The dimple VR was less than 0.75% and the A1 was greater than 0.655. The D / B ratio was less than 95, meaning the surface hardness of the intermediate layer-covered ball was harder than that of the core. As a result, the ball was hit with a driver (W#1) at a head speed (HS) of 54 m / s, resulting in a significant decrease in flight distance, a low launch angle on approach shots that was difficult for amateurs to hit, and the ball also lacked a satisfactory soft feel. Comparative Example 13 has a three-piece structure in which the surface hardness of the ball is softer than that of the intermediate layer-covered ball. The surface hardness of the intermediate layer-covered ball is also harder than that of the core. As a result, the launch angle on approach is too low, making the ball difficult for amateurs to hit, and the feel is also inferior. Comparative Example 14 had a three-piece structure in which the surface hardness of the ball was softer than that of the intermediate layer-covered ball. The dimple VR was less than 0.75% and the A1 was greater than 0.655. Furthermore, the initial ball velocity was less than 75.0 m / s, and the surface hardness of the intermediate layer-covered ball was greater than the surface hardness of the core. As a result, the ball achieved short distances when hit with a driver (W#1), a head speed (HS) of 40 m / s, and an iron (I#6), and the launch angle on approach shots was too low, making it difficult for amateurs to hit. Furthermore, the ball felt hard and unrewarding. Comparative Example 15 is a golf ball with a two-piece structure intended for use at driving ranges, and has an initial ball velocity of less than 75.0 m / s. As a result, the initial ball velocity is low under all hitting conditions. The flight distance when hit with a driver (W#1) at a head speed (HS) of 54 m / s is too low, and the flight distance is also reduced under other hitting conditions. Furthermore, as a game ball to be used during a round, the launch angle on approach is too low, making it difficult for amateurs to hit. Furthermore, the feel at impact is poor. [Explanation of symbols]

[0141] G Golf Ball 1 core 2. Enclosure Layer 3. Middle class 4 Cover D dimple

Claims

1. A multi-piece solid golf ball has a core, a single or multiple envelope layer, a single intermediate layer, and a single cover, with numerous dimples formed on the outer surface of the cover, wherein the core is made of a rubber material, and the envelope layer, intermediate layer, and cover are made of a resin material, and the relationship between the surface hardness of the ball, the envelope layer-covered sphere, and the intermediate layer-covered sphere satisfies the following formula (1-a) and the following formula (1-b): (Surface hardness of ball)>(Surface hardness of envelope layer-coated sphere) (1-a) (Surface hardness of ball)>(Surface hardness of intermediate layer-coated sphere) (1-b) (However, hardness refers to Shore C hardness.) and the relationship between the surface hardness of the core, the envelope layer-coated sphere, and the intermediate layer-coated sphere satisfies the following formula (2-a) or the following formula (2-b): (surface hardness of envelope layer-coated sphere) < (surface hardness of core) (2-a) (Surface hardness of intermediate layer-coated sphere) < (Surface hardness of core) (2-b) (However, hardness refers to Shore C hardness.) When at least one of the following equations is satisfied, and the initial velocity of the ball is 75.0 to 77.724 m / s, and the ratio CL1 / CD1 of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm is A1, the ratio CL2 / CD2 of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm is A2, and the ratio CL3 / CD3 of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm is A3, then the following two equations are satisfied: 0.590≦A1≦0.655, and (A2+A3) / 2≧0.670 and the volume fraction VR of the dimples is 0.75 to 0.89%, and the total volume of the dimples is D (mm 3 ), when the ball is subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf), the deflection amount is B (mm), and the following formula is used: 95≦D / B≦140 A multi-piece solid golf ball characterized by satisfying the above.

2. 2. The multi-piece solid golf ball according to claim 1, wherein the value of A1 is 0.590 to 0.613, the value of A2 is 0.635 to 0.668, and the value of A3 is 0.695 to 0.

734.

3. 2. The multi-piece solid golf ball according to claim 1, wherein the value of A1 is 0.614 to 0.655, the value of A2 is 0.669 to 0.750, and the value of A3 is 0.735 to 0.

815.

4. 3. The multi-piece solid golf ball according to claim 1, wherein the value of (A2+A3) / 2 is 0.670 to 0.

783.

5. 3. The multi-piece solid golf ball according to claim 1, wherein the cover is formed primarily from an ionomer resin.

6. The relationship between the surface hardness of each sphere is given by the following formula: (Surface hardness of ball) > (Surface hardness of intermediate layer-coated sphere) > (Surface hardness of envelope layer-coated sphere) < (Surface hardness of core) (However, hardness refers to Shore C hardness.) 3. The multi-piece solid golf ball according to claim 1, wherein the following is satisfied:

7. In the hardness distribution of the core, the Shore C hardness at the center of the core is Cc, the Shore C hardness at the midpoint M between the center and the surface of the core is Cm, the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm inward from the midpoint M are Cm-2, Cm-4, and Cm-6, respectively, the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm outward from the midpoint M are Cm+2, Cm+4, and Cm+6, respectively, and the Shore C hardness of the surface of the core is Cs. The following areas A to F are then defined: ・Area A: 1 / 2×2×(Cm-4-Cm-6) ・Area B: 1 / 2×2×(Cm-2-Cm-4) ・Area C: 1 / 2×2×(Cm-Cm-2) ・Area D: 1 / 2 x 2 x (Cm+2-Cm) ・Area E: 1 / 2 x 2 x (Cm+4-Cm+2) ・Area F: 1 / 2×2×(Cm+6-Cm+4) Regarding {(Area D+Area E)-(Area A+Area B)}≧4.0 3. The multi-piece solid golf ball according to claim 1, wherein the following is satisfied:

8. In the hardness distribution of the core, the following formula (Cs-Cc)≧20 8. The multi-piece solid golf ball of claim 7, which satisfies the following:

9. In the hardness distribution of the core, the following formula (Cs-Cc) / (Cm-Cc)≧4.0 8. The multi-piece solid golf ball of claim 7, which satisfies the following:

10. In the hardness distribution of the core, the following formula Area E > Area D > Area C 8. The multi-piece solid golf ball of claim 7, which satisfies the following:

11. The core comprises the following components (A) to (D): (A) Base rubber (B) Organic peroxide (C) Water or a metal monocarboxylate (D) sulfur 3. The multi-piece solid golf ball according to claim 1, which is formed from a rubber composition containing

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