Multi-piece solid golf ball

Abstract

To provide a golf ball suppressing a distance that a long hitter loses when hitting with a driver, but not so suppressing the distance that an average hitter loses when hitting with a driver.SOLUTION: A multi-piece solid golf ball includes a core, an envelope layer, an intermediate layer and a cover, and has a large number of dimples formed on the outer surface of the cover. The core is formed of a single-layer or multilayer rubber composition, the envelope layer is formed of a single-layer or multilayer resin composition, and the intermediate layer and the cover are each formed of a single-layer resin composition. The golf ball is characterized in that a relation between an initial velocity of an intermediate layer-encased sphere and an initial velocity of the ball satisfies the following formula: (Initial velocity of ball)<(Initial velocity of intermediate layer-encased sphere), an amount of deflection when a prescribed load is applied to the ball is optimized, and a lift coefficient and a drag coefficient at a given Reynolds number and spin rate of the dimples are set within a specified range.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a multi-piece solid golf ball which comprises a core, an envelope layer, a mid layer and a cover, the cover having a large number of dimples formed on its outer surface. [Background technology]

[0002] In March 2022, the R&A and the USGA notified golf ball manufacturers that they would begin research to reduce the flying distance of long hitters by changing the test conditions for the overall distance standard (ODS) of golf balls in the future. For this reason, rather than simply reducing the flying distance, it is preferable to create a golf ball that reduces the impact on play other than the loss of flying distance when hitting with a driver by increasing the distance by which the long hitter loses the flying distance when hitting with an iron, while reducing the distance by which the long hitter loses the flying distance when hitting with a driver. In addition, it is desirable to have a high level of spin characteristics for short games so that professionals and advanced players do not feel uncomfortable when using golf balls with reduced flying distance due to the above changes.

[0003] In the past, the following Patent Documents 1 to 4 have proposed golf balls that combine a low trajectory dimple design with the ball surface to significantly reduce the flight distance at high head speeds while minimizing the loss in flight distance at low head speeds in proportion to the reduction in high head speed. Patent Documents 5 to 8 have proposed golf balls with a flight distance that satisfies professionals and advanced players, in which the ball has a four-layer structure consisting of a core, an envelope layer, an intermediate layer, and a cover, the relationship between the initial velocity of the ball and the intermediate layer-covered sphere is optimized, and the core hardness gradient and amount of deflection are specified.

[0004] However, the golf balls of Patent Documents 1 to 4 have too short a flight distance when hit with a driver at a high head speed. Also, the golf balls of Patent Documents 5 to 8 are intended to increase the flight distance when hit with a driver (W#1), and are not intended to reduce the flight distance of long hitters. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-218160 A [Patent Document 2] JP 2011-218161 A [Patent Document 3] JP 2011-218162 A [Patent Document 4] JP 2011-240125 A [Patent Document 5] JP 2007-319667 A [Patent Document 6] JP 2008-068077 A [Patent Document 7] JP 2009-095364 A [Patent Document 8] JP 2012-071163 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a golf ball that does not simply reduce the distance traveled, but reduces the distance that a long hitter loses in distance when hitting with a driver, but does not reduce the distance that an average hitter loses in distance when hitting with a driver, in response to the possibility that the rules will be changed in the future to restrict the distance traveled by long hitters by changing the test conditions for the overall distance standard (ODS) of golf balls. [Means for solving the problem]

[0007] The inventors of the present invention have conducted extensive research to achieve the above object, and have found that by forming a ball structure having a core, an envelope layer, an intermediate layer, and a cover (outermost layer), in which the initial velocity of the intermediate layer-covered sphere is faster than the initial velocity of the ball, by setting the deflection of the entire ball when a certain load is applied to a relatively small amount, and by forming dimples on the surface of the ball by a special dimple design, the distance traveled by a driver (W#1) when hit by a long hitter is reduced, but the distance traveled by an average hitter with a W#1 is not reduced so much, and thus the present invention has been completed. The golf ball of the present invention also has high controllability in short games, and is also excellent in durability against cracking when hit repeatedly.

[0008] In addition, the above-mentioned "long hitter" refers to a user whose head speed when hitting with a driver (W#1) is approximately 50 m / s or more, and the above-mentioned "average hitter" refers to a user whose head speed when hitting with a driver (W#1) is approximately 45 m / s or less.

[0009] Accordingly, the present invention provides a multi-piece solid golf ball as follows: 1. A multi-piece solid golf ball comprising a core, an envelope layer, an intermediate layer, and a cover, and having a number of dimples formed on the outer surface of the cover, wherein the core is formed of a single layer or multiple layers of a rubber composition, the envelope layer is formed of a single layer or multiple layers of a resin composition, and the intermediate layer and the cover are both formed of a single layer of a resin composition, and the relationship between the initial velocity of the intermediate layer-covered sphere and the initial velocity of the ball satisfies the following formula: (Initial speed of ball)<(Initial speed of middle layer covered sphere) and the amount of deflection when the ball is subjected to an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is 3.0mm or less. Also, 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 2,800rpm 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 2,900rpm 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 3,100rpm is A3, the following two equations are satisfied: 0.590≦A1≦0.640, and (A2+A3) / 2≧0.670 A multi-piece solid golf ball comprising: 2. The multi-piece solid golf ball according to the above item 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. The multi-piece solid golf ball according to the above item 2, wherein the value of A1 is 0.614 to 0.640, 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 the above 1 or 2, wherein the value of (A2+A3) / 2 is 0.670 to 0.783. 5. The following three equations: (Initial velocity of the intermediate layer-coated sphere) - (Initial velocity of the surrounding layer-coated sphere) ≦ 0.70 (m / s) (Initial velocity of the enveloped sphere) - (Initial velocity of the core) ≧ 0.20 (m / s) 1.00≦(initial velocity of intermediate layer-coated sphere)-(initial velocity of core)≦1.60(m / s) 3. A multi-piece solid golf ball according to claim 1 or 2, which satisfies the above requirements. 6. The following formula: 0.65≦(initial velocity of the enveloped sphere)-(initial velocity of the core)≦1.00(m / s) 3. A multi-piece solid golf ball according to claim 1 or 2, which satisfies the above requirements. 7. The following formula: Ball surface hardness <Surface hardness of intermediate layer covered sphere> Surface hardness of envelope layer covered sphere> Core surface hardness (Note that the surface hardness of each sphere mentioned above means Shore C hardness.) 3. A multi-piece solid golf ball according to claim 1 or 2, which satisfies the above requirements. 8. The multi-piece solid golf ball according to the above 1 or 2, wherein the intermediate layer contains an inorganic granular filler and the specific gravity of the resin material of the intermediate layer is 1.05 or more. 9. The multi-piece solid golf ball according to 1 or 2 above, wherein the difference between the specific gravity of the cover and the specific gravity of the intermediate layer is within 0.15. 10. The multi-piece solid golf ball according to the above 1 or 2, wherein the resin composition of the intermediate layer contains a high-acid ionomer resin having an acid content of 16% by mass or more. 11. The following formula: Cover thickness < Intermediate layer thickness ≦ Enveloping layer thickness 3. A multi-piece solid golf ball according to claim 1 or 2, which satisfies the above requirements. 12. In the hardness distribution of the above 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 2mm, 4mm, and 6mm inward from the midpoint M are Cm-2, Cm-4, and Cm-6, respectively, the Shore C hardnesses at positions 2mm, 4mm, and 6mm outward from the center 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 E+Area F)-(Area A+Area B)≧1.0 3. A multi-piece solid golf ball according to claim 1 or 2, which satisfies the above requirements. 13. The following formula: 35≦(Surface hardness of intermediate layer-coated sphere)-(Center hardness of core) (However, hardness refers to Shore C hardness.) 8. A multi-piece solid golf ball as described in 7 above which satisfies the above requirements. Effect of the Invention

[0010] According to the golf ball of the present invention, there is a possibility that the rules will be changed to restrict the distance of long hitters by changing the test conditions of the standard overall distance (ODS) of golf balls in the future from R&A and USGA. Instead of simply reducing the distance, the golf ball reduces the distance of the driver (W#1) when a long hitter hits the ball, but does not reduce the distance of the W#1 of an average hitter, so that it is possible to reduce the impact on play other than the reduction in the distance of the driver when a long hitter hits the ball. Furthermore, when used by professionals and advanced players, the golf ball of the present invention has a lower driver (W#1) distance than a conventional tour ball, but has high short game properties by keeping the level of spin in the short game at the same level. Furthermore, the golf ball of the present invention has excellent crack resistance when hit repeatedly. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view of a golf ball according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram illustrating areas A to F of the core hardness distribution, using core hardness distribution data of Example 1. [Diagram 3] 2 is a graph showing the core hardness distributions 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 5 to 9. [Diagram 5] FIG. 2 shows the arrangement (pattern) of dimples (1) to (4) used in Examples 1 to 4 and Comparative Examples 1 to 9, where (A) shows a plan view of the dimples and (B) shows a side view thereof. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will now be described in further detail. As shown in Fig. 1, the multi-piece solid golf ball of the present invention is a golf ball G having four or more layers, including a core 1, an envelope layer 2 enclosing the core, an intermediate layer 3 enclosing the envelope layer, and a cover 4 enclosing the intermediate layer. A large number of dimples D are formed on the surface of the cover 4 in order to achieve the aerodynamic characteristics targeted by the present invention. Although not shown, a coating layer is usually formed on the surface of the cover 4 by painting. The cover 4 is positioned as the outermost layer in the layer structure of the golf ball, excluding the coating layer. The core 1 and the envelope layer 2 are not limited to being formed as a single layer, but may be formed as two or more layers, while the intermediate layer 3 or the cover 4 is formed as a single layer.

[0013] The core is obtained by vulcanizing a rubber composition mainly made of rubber material. If the core material is not a rubber composition, the core will have low resilience, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1) or iron. This rubber composition is usually made mainly of base rubber, and is obtained by compounding co-crosslinking agents, crosslinking initiators, inert fillers, antioxidants, organic sulfur compounds, etc.

[0014] The base rubber may include a diene rubber. Examples of the diene rubber include polybutadiene, natural rubber, isoprene rubber, ethylene propylene diene rubber, etc. These base rubbers may be used alone or in combination of two or more.

[0015] The co-crosslinking agent is an α,β-unsaturated carboxylic acid and / or a metal salt thereof. Specific examples of the unsaturated carboxylic acid 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 include, for example, 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 and acrylic acid, with zinc acrylate being particularly preferred.

[0016] The unsaturated carboxylic acid and / or metal salt thereof is blended in an amount of usually 5 parts by weight or more, preferably 15 parts by weight or more, and more preferably 25 parts by weight or more, and usually up to 60 parts by weight, preferably up to 50 parts by weight, and more preferably up to 40 parts by weight, per 100 parts by weight of the base rubber. If the blended amount is too high, the ball may become too hard, resulting in an unbearable feel on impact, whereas if the blended amount is too low, the resilience may decrease.

[0017] The crosslinking initiator is usually an organic peroxide. As the organic peroxide, it is preferable to use an organic peroxide with a relatively high thermal decomposition temperature, specifically, a high-temperature organic peroxide with a 1-minute half-life temperature of about 165 to 185°C is used, and for example, dialkyl peroxides can be mentioned. As the dialkyl peroxides, for example, dicumyl peroxide ("Percumyl D" manufactured by NOF Corp.), 2,5-dimethyl-2,5-di(t-butylperoxy)hexane ("Perhexa 25B" manufactured by NOF Corp.), di(2-t-butylperoxyisopropyl)benzene ("Perbutyl P" manufactured by NOF Corp.), etc. can be mentioned, and dicumyl peroxide can be preferably used. These may be used alone or in combination of two or more kinds. The half-life is one of the indicators showing the degree of the decomposition speed of the organic peroxide, and is indicated by the time required for the original organic peroxide to decompose and the amount of active oxygen to be reduced to 1 / 2. The vulcanization temperature of the rubber composition for the core is usually within the range of 120 to 190° C., and within this range, organic peroxides with a high one-minute half-life temperature of about 165° C. to 185° C. undergo thermal decomposition relatively slowly. According to 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 described later, by adjusting the amount of free radicals produced, which increases with the passage of vulcanization time.

[0018] As the inert filler, for example, zinc oxide, barium sulfate, calcium carbonate, etc. can be suitably used. These may be used alone or in combination of two or more. The amount of the filler to be mixed may be preferably 4 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 12 parts by mass or more, per 100 parts by mass of the base rubber. The upper limit of the amount to be mixed may be preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of the base rubber. If the amount to be mixed is too large or too small, it may not be possible to obtain the appropriate mass and suitable resilience.

[0019] 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 kinds.

[0020] The amount of antioxidant is not particularly limited, but is preferably at least 0.05 parts by weight, more preferably at least 0.1 parts by weight, and the upper limit is preferably no more than 1.0 part by weight, more preferably no more than 0.7 parts by weight, and even more preferably no more than 0.5 parts by weight, per 100 parts by weight of base rubber. If the amount is too large or too small, the appropriate core hardness gradient may not be obtained, and suitable resilience, durability, and low spin effect on full shots may not be obtained.

[0021] The organic sulfur compound can be blended in order to control the resilience of the core.Specifically, it is recommended to blend thiophenol, thionaphthol, halogenated thiophenol or their metal salts as the organic sulfur compound.More specifically, it can be pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, zinc salt of pentachlorothiophenol, diphenyl polysulfide, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, dithiobenzoyl polysulfide, etc., which have 2 to 4 sulfurs, and it is particularly preferable to use the zinc salt of pentachlorothiophenol and diphenyl disulfide.

[0022] The upper limit of the amount of the organic sulfur compound is preferably 5 parts by weight or less, more preferably 4 parts by weight or less, even more preferably 3 parts by weight or less, and most preferably 2 parts by weight or less, per 100 parts by weight of the base rubber. If the amount is too high, the core may become too soft, or the core may become too resilient, resulting in too long a flight distance when hit with a driver by a long hitter. On the other hand, the lower limit of the amount is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, and even more preferably 0.3 parts by weight or more, per 100 parts by weight of the base rubber. If the amount is too low, the core may become too resilient, resulting in too short a flight distance when hit with a driver by an average hitter and when hit with an iron by both a long hitter and an average hitter.

[0023] Sulfur can also be compounded into the rubber composition. Specific examples of sulfur include products under the trade names "Sunmix S-80N" (manufactured by Sanshin Chemical Industry Co., Ltd.) and "Sulfax-5" (manufactured by Tsurumi Chemical Industry Co., Ltd.). The addition of sulfur can increase the hardness difference of the core. However, if the amount of sulfur compounded is too much, the resilience may be significantly reduced and the durability against repeated impact may be reduced.

[0024] The core can be produced by vulcanizing and curing a rubber composition containing the above-mentioned components. For example, the rubber composition is kneaded using a kneading machine such as a Banbury mixer or a roll, compression molded or injection molded using a core mold, and the molded body is appropriately heated at a temperature sufficient for the organic peroxide and co-crosslinking agent to act, that is, 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes, to cure the molded body.

[0025] In the present invention, the core is formed in a single layer or multiple layers, but is preferably formed in a single layer. If a rubber core is made of multiple layers, peeling may occur at the interface when repeatedly struck, leading to early cracking.

[0026] The diameter of the core is preferably 35.1 mm or more, more preferably 35.3 mm or more, and even more preferably 35.4 mm or more. The upper limit of this diameter is preferably 41.3 mm or less, more preferably 39.2 mm or less, and even more preferably 38.3 mm or less. If the core diameter is too small, the initial velocity of the ball may be too low, or the deflection of the entire ball may be small, and the spin rate of the ball may increase during a full shot, making it impossible for an average hitter to achieve the desired flight distance when hitting with a driver (W#1). On the other hand, if the core diameter is too large, the spin rate of the ball may increase during a full shot, making it impossible for an average hitter to achieve the desired flight distance, or the durability against cracking may be poor when hitting repeatedly.

[0027] The deflection (mm) of the core when an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is applied is not particularly limited, but is preferably 2.9mm or more, more preferably 3.2mm or more, and even more preferably 3.5mm or more, with the upper limit being preferably 5.0mm or less, more preferably 4.4mm or less, and even more preferably 4.2mm or less. If the deflection of the core is too small, i.e., if the core is too hard, the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1), or the hitting feel may be too hard. On the other hand, if the deflection of the core is too large, i.e., if the core is too soft, the resilience of the ball may be too low, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1), or the hitting feel may be too soft, or the cracking durability may be poor when hitting repeatedly.

[0028] 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.

[0029] The center hardness (Cc) of the core is preferably 50 or more, more preferably 52 or more, and even more preferably 54 or more, with the upper limit being preferably 61 or less, more preferably 59 or less, and even more preferably 57 or less. If this value is too large, the average hitter will not be able to achieve the desired flight distance when hitting with a driver (W#1), and the hit feeling may be too hard. On the other hand, if the value is too small, the resilience will be reduced and the ball will not fly, the average hitter will not be able to achieve the desired flight distance when hitting with a driver (W#1), or the crack resistance when hitting repeatedly may be poor.

[0030] The hardness (Cm-6) 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 51 or more, more preferably 53 or more, and even more preferably 55 or more, and there is no particular upper limit either, but is preferably 61 or less, more preferably 59 or less, and even more preferably 57 or less. Any deviation from these hardnesses may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0031] The hardness (Cm-4) at a position 4 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 52 or more, more preferably 54 or more, and even more preferably 56 or more, and there is no particular upper limit either, but is preferably 63 or less, more preferably 61 or less, and even more preferably 59 or less. Any deviation from these hardnesses may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0032] The hardness (Cm-2) at a position 2 mm inward from the middle position M of the core is not particularly limited, but is preferably 53 or more, more preferably 55 or more, and even more preferably 57 or more, and the upper limit is not particularly limited, but is preferably 63 or less, more preferably 61 or less, and even more preferably 59 or less. If the hardness deviates from these ranges, it may cause the same disadvantageous results as those described for the center hardness (Cc) of the core. If the hardness deviates from these ranges, it may cause the same disadvantageous results as those described for the center hardness (Cc) of the core.

[0033] The cross-sectional hardness (Cm) of the core at the middle position M is not particularly limited, but is preferably at least 55, more preferably at least 57, and even more preferably at least 59. There is also no particular upper limit, but it is preferably at most 66, more preferably at most 64, and even more preferably at most 62. Any deviation from these hardness limits may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0034] The surface hardness (Cs) of the core is preferably 78 or more, more preferably 80 or more, and even more preferably 82 or more, with the upper limit being preferably 90 or less, more preferably 88 or less, and even more preferably 86 or less. If this value is too large, the durability against cracking during repeated impacts may be poor, or the hitting feel may be too hard. On the other hand, if this value is too small, the resilience may be low and the ball may not fly, or the amount of spin on a full shot may be too high, making it difficult for an average hitter to achieve the desired flight distance when hitting with a driver (W#1).

[0035] 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 60 or more, more preferably 62 or more, and even more preferably 64 or more, and there is no particular upper limit, but is preferably 71 or less, more preferably 69 or less, and even more preferably 67 or less. Any deviation from these hardnesses may result in the same adverse effects as those described for the surface hardness (Cs) of the core.

[0036] The hardness (Cm+4) at a position 4 mm outward from the middle position M of the core is not particularly limited, but is preferably at least 65, more preferably at least 67, and even more preferably at least 69, and there is no upper limit either, but is preferably at most 78, more preferably at most 76, and even more preferably at most 74. Any deviation from these hardness limits may result in the same adverse effects as those described for the surface hardness (Cs) of the core.

[0037] The hardness (Cm+6) at a position 6 mm outward from the middle position M of the core is not particularly limited, but is preferably at least 70, more preferably at least 72, and even more preferably at least 74, and there is no upper limit either, but is preferably at most 83, more preferably at most 81, and even more preferably at most 79. Any deviation from these hardness limits may result in the same adverse effects as those described for the surface hardness (Cs) of the core.

[0038] 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 E+area F)-(area A+area B) is preferably 1.0 or more, more preferably 2.0 or more, and more preferably 4.0 or more, and the upper limit is preferably 20.0 or less, more preferably 16.0 or less, and even more preferably 12.0 or less. If this value is too large, the durability against cracking may deteriorate when repeatedly hit. On the other hand, if this value is too small, the spin amount at the time of a full shot increases, and the desired flight distance at the time of hitting with a driver (W#1) by an average hitter may not be obtained.

[0039] In addition, the value of (area D + area E) - (area B + area C) is preferably 1.0 or more, more preferably 2.0 or more, and more preferably 3.0 or more, and the upper limit is preferably 20.0 or less, more preferably 16.0 or less, and even more preferably 12.0 or less. If this value is too large, the durability against cracking when repeatedly hit may deteriorate. On the other hand, if this value is too small, the spin amount at the time of a full shot may increase, and the desired flight distance may not be obtained when hitting with a driver (W#1) by an average hitter.

[0040] The above areas A to F are calculated using the following formula: Area A<Area C<(Area E+Area F), and Area B<Area C<(Area E+Area F) It is preferable that the following formula is satisfied, and more preferable that the following formula is satisfied: Area A<Area C<Area D<(Area E+Area F), and Area B<Area C<Area D<(Area E+Area F) If these relationships are not satisfied, the amount of spin on a full shot increases, and an average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1).

[0041] 2 shows a schematic diagram explaining areas A to F using the core hardness distribution data of Example 1. In this way, areas A to F are the areas of triangles whose bases are the differences in each specific distance and whose heights are the differences in hardness at each position.

[0042] The initial velocity of the core is preferably 75.5 m / s or more, more preferably 75.9 m / s or more, and even more preferably 76.2 m / s or more, and the upper limit is preferably 77.2 m / s or less, more preferably 76.9 m / s or less, and even more preferably 76.6 m / s or less. If this initial velocity value is too high, the initial velocity of the ball will be too high and may violate the rules. On the other hand, if the initial velocity of the core is too low, the resilience of the ball will be low at the time of a full shot, or the amount of spin will be high, and the desired flight distance may not be obtained when an average hitter hits with a driver (W#1). In this case, the initial velocity value is a value measured by a COR type initial velocity meter of the same type as that of R&A. Specifically, a COR type initial velocity device manufactured by Hye Precision in the United States is used. As conditions, the air pressure is changed to four levels during measurement, a relationship between the entrance velocity and COR is constructed, and the initial velocity at the entrance velocity of 43.83 m / s is obtained from this relationship. The measurement environment for the COR type muzzle velocity device is as follows: a ball that has been kept in a thermostatic chamber adjusted to 23.9±1°C for more than three hours is used, and measurements are taken at room temperature of 23.9±2°C.

[0043] Next, the envelope layer will be described. The material hardness of the surrounding layer is not particularly limited, but is preferably 72 or more, more preferably 75 or more, and even more preferably 78 or more in Shore C hardness, with the upper limit being preferably 92 or less, more preferably 90 or less, and even more preferably 88 or less. The Shore D hardness is preferably 47 or more, more preferably 49 or more, and even more preferably 51 or more, with the upper limit being preferably 62 or less, more preferably 60 or less, and even more preferably 57 or less.

[0044] The surface hardness of a sphere having a core covered with an envelope layer is preferably 80 or more, more preferably 83 or more, and even more preferably 86 or more, in Shore C hardness, with the upper limit being preferably 97 or less, more preferably 95 or less, and even more preferably 93 or less. The surface hardness of a sphere having a core covered with an envelope layer is preferably 53 or more, more preferably 55 or more, and even more preferably 57 or more, with the upper limit being preferably 68 or less, more preferably 66 or less, and even more preferably 63 or less.

[0045] When the surrounding layer is made up of multiple layers, the hardness values ​​mentioned above refer to the hardness of the outer surrounding layer, and the surface hardness refers to the surface hardness of the coated sphere covered with the outer surrounding layer.

[0046] If the material hardness and surface hardness of the surrounding layer are too soft, the ball may spin too much on a full shot, or the initial velocity may be too low, making it difficult for an average hitter to achieve the desired distance when hitting with a driver (W#1).On the other hand, if the material hardness and surface hardness of the surrounding layer are too hard, the ball may feel too hard on impact, or may have poor durability against cracking when hit repeatedly.

[0047] 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. On the other hand, the upper limit of the thickness of the envelope layer is preferably 2.0 mm or less, more preferably 1.6 mm or less, and even more preferably 1.4 mm or less. If the thickness of the envelope layer is out of the above range, the low spin effect during a full shot may be insufficient, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1). If the envelope layer is too thin, the durability against cracking during repeated hitting may be poor.

[0048] Furthermore, it is preferable that the thickness of the envelope layer satisfies the condition (thickness of the intermediate layer)<(thickness of the envelope layer) in relation to the thickness of the intermediate layer described below.

[0049] The envelope layer is made of a single layer or multiple layers of a resin material, and is an essential member for ensuring excellent durability against repeated impacts. The material for this envelope layer is not particularly limited, but known resins can be used. Particularly preferred examples of the material include the following components (a) to (c): (a) an olefin-unsaturated carboxylic acid binary random copolymer and / or a metal ion neutralized product of an olefin-unsaturated carboxylic acid binary random copolymer, (b) a base resin containing an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer and / or a metal ion neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer in a mass ratio of 100:0 to 0:100; (c) A resin composition in which a non-ionomeric thermoplastic elastomer and (c) a non-ionomeric thermoplastic elastomer are blended in a mass ratio of 100:0 to 0:100 can be exemplified.

[0050] As for the components (a) to (c), for example, the resin material for the intermediate layer described in JP 2010-253268 A can be suitably used, which is a material that is flexible and has high resilience, and is also suitable for achieving low spin rate characteristics on full shots.

[0051] Any additives can be appropriately blended into the above resin material depending on the application. For example, various additives such as pigments, dispersants, antioxidants, UV absorbers, and light stabilizers can be added. When these additives are blended, the blending amount is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and the upper limit is preferably 10 parts by mass or less, more preferably 4 parts by mass or less, relative to 100 parts by mass of the total of the above base resins.

[0052] The resin material may contain an inorganic granular filler. The inorganic granular filler is not particularly limited, but zinc oxide, barium sulfate, titanium dioxide, etc. may be appropriately used. From the viewpoint of excellent durability against cracking due to repeated impacts, it is preferable to use barium sulfate, and particularly preferable to use precipitated barium sulfate.

[0053] The average particle size of the inorganic granular filler is not particularly limited, but is preferably 0.01 to 100 μm, more preferably 0.1 to 10 μm. If the average particle size of the inorganic granular filler is too small or too large, dispersibility during material preparation may deteriorate. The average particle size refers to the particle size measured by a particle size distribution measuring device after dispersing the inorganic granular filler in an aqueous solution together with a suitable dispersing agent.

[0054] The amount of the inorganic granular filler to be mixed is not particularly limited, but is preferably 30 parts by mass or less per 100 parts by mass of the base resin of the surrounding layer material. The specific gravity of the surrounding layer is preferably within the range of 0.95 to 1.25.

[0055] The initial velocity of a sphere in which a core is covered with an envelope layer (enveloping layer-covered sphere) is preferably 76.0 m / s or more, more preferably 76.5 m / s or more, and even more preferably 77.0 m / s or more, with the upper limit being preferably 78.0 m / s or less, more preferably 77.7 m / s or less, and even more preferably 77.5 m / s or less. If this initial velocity value is too high, the initial velocity of the ball becomes too high and may violate the rules. On the other hand, if this initial velocity is too low, the resilience of the ball may be low or the amount of spin may be high during a full shot, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1). The initial velocity in this case is the same as that used in the measurement of the initial velocity of the core described above under the same device and conditions.

[0056] Next, the intermediate layer will be described. The material hardness of the intermediate layer is not particularly limited, but is preferably 90 or more, more preferably 92 or more, and even more preferably 93 or more in Shore C hardness, with the upper limit being preferably 100 or less, more preferably 98 or less, and even more preferably 96 or less. The Shore D hardness is preferably 64 or more, more preferably 66 or more, and even more preferably 68 or more, with the upper limit being preferably 75 or less, more preferably 72 or less, and even more preferably 70 or less.

[0057] The surface hardness of a sphere (intermediate layer coated sphere) obtained by coating an envelope layer coated sphere with an intermediate layer, in Shore C hardness, is preferably 95 or more, more preferably 96 or more, and even more preferably 97 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 68 or more, more preferably 69 or more, and even more preferably 70 or more, with the upper limit being preferably 78 or less, more preferably 75 or less, and even more preferably 72 or less.

[0058] If the material hardness and surface hardness of these intermediate layers are softer than the above ranges, the spin rate on full shots will be too high, the initial velocity will be low, and the average hitter may not be able to achieve the desired distance when hitting with a driver (W#1).On the other hand, if the material hardness and surface hardness of the intermediate layers are harder than the above ranges, the durability against cracking due to repeated hits will be poor, or the hitting feel when hitting with a putter or on a short approach may be too hard.

[0059] The thickness of the intermediate layer is preferably 0.7 mm or more, more preferably 0.8 mm or more, and even more preferably 1.0 mm or more. On the other hand, the upper limit of the thickness of the intermediate layer is preferably 1.8 mm or less, more preferably 1.4 mm or less, and even more preferably 1.2 mm or less. In addition, it is preferable that the thickness of the intermediate layer is thicker than the cover described below. If the thickness of the intermediate layer is out of the above range or is thinner than the cover, the effect of reducing the spin of the ball when hit with a driver (W#1) may be insufficient, and the average hitter may not be able to achieve the desired flight distance. In addition, if the intermediate layer is too thin, the crack durability during repeated hits may be poor.

[0060] It is preferable to use an ionomer resin as the main material for the intermediate layer.

[0061] The ionomer resin material preferably contains a high-acid content ionomer resin having an unsaturated carboxylic acid content (also referred to as "acid content") of 16% by mass or more.

[0062] The content of the high acid content ionomer resin is preferably 20% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, with the upper limit being preferably 100% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less, based on 100% by mass of the resin material. If the amount of the high acid content ionomer resin is too small, the ball may have a large spin rate upon full shot, resulting in a loss of flight distance. On the other hand, if the amount of the high acid content ionomer resin is too large, the durability against repeated impacts may be poor.

[0063] In addition, when an ionomer resin is used as the main material, it is desirable to use a mixture of zinc-neutralized ionomer resin and sodium-neutralized ionomer resin as the main material. The blending ratio of zinc-neutralized / sodium-neutralized (mass ratio) is 5 / 95 to 95 / 5, preferably 10 / 90 to 90 / 10, and more preferably 15 / 85 to 85 / 15. If the Zn-neutralized ionomer and the Na-neutralized ionomer are not included in this ratio, the resilience may be too low to obtain the desired flight, or the crack resistance may be poor when repeatedly struck at room temperature, or the crack resistance may be poor at low temperatures (below zero).

[0064] Any additives can be appropriately blended into the intermediate layer material depending on the application. For example, various additives such as pigments, dispersants, anti-aging agents, UV absorbers, and light stabilizers can be added. When these additives are blended, the blending amount is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and the upper limit is preferably 10 parts by mass or less, more preferably 4 parts by mass or less, relative to 100 parts by mass of the base resin.

[0065] It is preferable to polish the surface of the intermediate layer material to improve adhesion with the polyurethane that is preferably used in the cover material described below. Furthermore, after the polishing process, it is preferable to apply a primer (adhesive) to the intermediate layer surface or to add an adhesion enhancer to the material.

[0066] The material of the intermediate layer may contain an inorganic granular filler. This inorganic granular filler is not particularly limited, but zinc oxide, barium sulfate, titanium dioxide, etc. may be appropriately used. From the viewpoint of excellent resistance to cracking caused by repeated impacts, it is preferable to use barium sulfate, and particularly preferable to use precipitated barium sulfate.

[0067] The average particle size of the inorganic granular filler is not particularly limited, but is preferably 0.01 to 100 μm, more preferably 0.1 to 10 μm. If the average particle size of the inorganic granular filler is too small or too large, dispersibility during material preparation may deteriorate. The average particle size refers to the particle size measured by a particle size distribution measuring device after dispersing the inorganic granular filler in an aqueous solution together with a suitable dispersing agent.

[0068] The amount of the inorganic granular filler is not particularly limited, but is preferably 0 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of the base resin of the intermediate layer material. The upper limit is also not particularly limited, but is 50 parts by mass or less, preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less. If the amount of the inorganic granular filler is too small, the durability against cracking due to repeated impacts may deteriorate. On the other hand, if the amount of the inorganic granular filler is too large, the resilience of the ball may decrease, or the spin amount of the ball during a full shot may increase, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1).

[0069] The specific gravity of the intermediate layer is preferably 1.05 or more, more preferably 1.07 or more, and even more preferably 1.09 or more, with the upper limit being preferably 1.25 or less, more preferably 1.20 or less, and even more preferably 1.15 or less. If the specific gravity of the intermediate layer is too low, the durability against cracking caused by repeated impacts may be poor. On the other hand, if the specific gravity of the intermediate layer is too high, the resilience of the ball may be low, or the amount of spin of the ball may be high on a full shot, preventing an average hitter from achieving the desired flight distance when hitting with a driver (W#1).

[0070] The initial velocity of the sphere (intermediate-layer-coated sphere) in which the intermediate layer is coated on the envelope-layer-coated sphere is preferably 77.0 m / s or more, more preferably 77.4 m / s or more, and even more preferably 77.7 m / s or more, with the upper limit being preferably 78.5 m / s or less, more preferably 78.2 m / s or less, and even more preferably 77.9 m / s or less. If this initial velocity value is too high, the initial velocity of the ball becomes too high and may violate the rules. On the other hand, if this initial velocity is too low, the resilience of the ball may be low or the amount of spin may be high on a full shot, and the average hitter may not achieve the desired flight distance when hitting with a driver (W#1). The initial velocity in this case is the same as that used in the measurement of the initial velocity of the core and envelope-layer-coated sphere described above under the same device and conditions.

[0071] Next, the cover will be described. The material hardness of the cover is not particularly limited, but the Shore C hardness is preferably 50 or more, more preferably 57 or more, and even more preferably 63 or more, with the upper limit being preferably 80 or less, more preferably 74 or less, and even more preferably 71 or less. The Shore D hardness is preferably 30 or more, more preferably 35 or more, and even more preferably 40 or more, with the upper limit being preferably 53 or less, more preferably 50 or less, and even more preferably 47 or less.

[0072] The surface hardness of a sphere (ball) obtained by covering an intermediate layer-covered sphere with a cover, in Shore C hardness, is preferably 73 or more, more preferably 78 or more, and even more preferably 83 or more, 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 50 or more, more preferably 53 or more, and even more preferably 56 or more, with the upper limit being preferably 70 or less, more preferably 65 or less, and even more preferably 60 or less.

[0073] If the material hardness and surface hardness of these covers are softer than the above ranges, the amount of spin will be too much on full shots, and the average hitter may not be able to achieve the desired distance when hitting with a driver (W#1). On the other hand, if the material hardness and surface hardness of the cover are harder than the above ranges, the spin will not be applied on approaches, or the abrasion resistance may be poor. In addition, the distance will be too great when a long hitter hits with a driver (W#1), and there is a risk that it will not comply with the new Overall Distance Standard (ODS) rules, which may be changed in the future.

[0074] The thickness of the cover is preferably 0.3 mm or more, more preferably 0.5 mm or more, and even more preferably 0.6 mm or more. On the other hand, the upper limit of the cover thickness is preferably 1.2 mm or less, more preferably 0.9 mm or less, and even more preferably 0.8 mm or less. If the cover is too thick, the resilience of the ball may be insufficient on a full shot, or the amount of spin may be increased, resulting in a lack of distance when hit with a driver (W#1) by an average hitter. On the other hand, if the cover is too thin, the abrasion resistance may be poor, or the spin may not be applied on an approach shot, resulting in a lack of controllability.

[0075] As the material for the cover, various urethane resins used in golf ball cover materials can be used from the viewpoints of spin controllability and abrasion resistance in the short game. Furthermore, from the viewpoint of mass production, it is preferable to use a resin material mainly composed of thermoplastic polyurethane. Furthermore, it is preferable to form the cover from a resin blend mainly composed of (I) thermoplastic polyurethane and (II) a polyisocyanate compound.

[0076] The total weight of the above components (I) and (II) is preferably 60% or more, and more preferably 70% or more, based on the total weight of the resin composition of the cover. The above components (I) and (II) are described in detail below.

[0077] Regarding the above (I) thermoplastic polyurethane, the structure of the thermoplastic polyurethane includes a soft segment made of a polymer polyol (polymeric glycol) which is a long-chain polyol, and a hard segment made of a chain extender and a polyisocyanate compound. Here, as the long-chain polyol used as the raw material, any one that has been used in the technology related to thermoplastic polyurethanes can be used, and there is no particular limitation. For example, polyester polyol, polyether polyol, polycarbonate polyol, polyester polycarbonate polyol, polyolefin polyol, conjugated diene polymer polyol, castor oil polyol, silicone polyol, vinyl polymer polyol, etc. can be mentioned. These long-chain polyols may be used alone or in combination of two or more kinds. Among these, polyether polyol is preferred in that it can synthesize a thermoplastic polyurethane with a high resilience modulus and excellent low-temperature properties.

[0078] As the chain extender, those used in conventional techniques related to thermoplastic polyurethanes can be suitably used, and for example, a low molecular weight compound having two or more active hydrogen atoms in the molecule that can react with an isocyanate group and a molecular weight of 400 or less is preferable. Examples of the chain extender include, but are not limited to, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, etc. Among these, as the chain extender, an aliphatic diol having 2 to 12 carbon atoms is preferable, and 1,4-butylene glycol is more preferable.

[0079] The polyisocyanate compound may be suitably used in the conventional technology related to thermoplastic polyurethane, and is not particularly limited. Specifically, one or more selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-(or) 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethyl xylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate may be used. However, some isocyanate species may be difficult to control the crosslinking reaction during injection molding. In the present invention, from the viewpoint of the balance between stability during production and the physical properties exhibited, 4,4'-diphenylmethane diisocyanate, which is an aromatic diisocyanate, is most preferred.

[0080] Specific examples of thermoplastic polyurethanes that can be used as the component (I) include commercially available products such as Pandex T8295, T8290, and T8260 (all manufactured by DIC Covestro Polymers).

[0081] Although not a required component, a thermoplastic elastomer other than the thermoplastic polyurethane can be blended as component (III) to the above components (I) and (II). By blending component (III) with the resin blend, it is possible to further improve the flowability of the resin blend and to enhance various physical properties required for a golf ball cover material, such as resilience and abrasion resistance.

[0082] There are no particular limitations on the composition ratio of the above components (I), (II) and (III). However, in order to fully and effectively exert the effects of the present invention, the mass ratio is preferably (I):(II):(III)=100:2-50:0-50, and more preferably (I):(II):(III)=100:2-30:8-50 (mass ratio).

[0083] Furthermore, various additives other than the components constituting the thermoplastic polyurethane may be blended into the above-mentioned resin blend as necessary. For example, pigments, dispersants, antioxidants, light resistance stabilizers, ultraviolet absorbers, release agents, etc. may be appropriately blended.

[0084] The specific gravity of the cover is preferably 1.00 or more, more preferably 1.03 or more, and even more preferably 1.06 or more, with the upper limit being preferably 1.20 or less, more preferably 1.17 or less, and even more preferably 1.14 or less. If the specific gravity of the cover is too low, the blend ratio of ionomers and the like may become high, resulting in poor abrasion resistance and poor crack resistance when repeatedly struck. On the other hand, if the specific gravity of the cover is too high, the amount of filler added becomes too high, resulting in too low resilience, and the average hitter may not be able to achieve the desired distance when striking with a driver (W#1).

[0085] The multi-piece solid golf ball formed by laminating the above-mentioned core, surrounding layer, intermediate layer, and cover (outermost layer) can be manufactured by a conventional method such as a known injection molding method. For example, the materials for the surrounding layer and intermediate layer are sequentially injected around the core using respective injection molds to obtain each covered sphere, and finally, the material for the cover, which is the outermost layer, is injection molded to obtain a multi-piece golf ball. Alternatively, the golf ball can be manufactured by encasing the covered sphere in two half cups that have been molded into a half-shell shape in advance and molding them under heat and pressure as each covered layer.

[0086] The deflection (mm) of the golf ball when subjected to an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is preferably 2.0mm or more, more preferably 2.3mm or more, and even more preferably 2.5mm or more. On the other hand, the upper limit of the deflection is preferably 3.0mm or less, more preferably 2.9mm or less. If the deflection of the golf ball is too small, i.e., the ball is too hard, the spin rate increases too much, and the average hitter may not achieve the desired flight distance when hitting with a driver (W#1), or the hitting feel may be too hard. On the other hand, if the deflection is too large, i.e., the ball is too soft, the hitting feel may be too soft, or the durability against cracking during repeated hitting may be poor.

[0087] The initial velocity of a sphere (ball) in which an intermediate layer-covered sphere is covered with a cover is preferably 76.8 m / s or more, more preferably 77.0 m / s or more, and even more preferably 77.2 m / s or more, with the upper limit being 77.724 m / s or less. If this initial velocity value is too high, it will not satisfy the official rules of R&A and USGA. On the other hand, if this initial velocity is too low, it may not be possible to achieve the desired flight distance when hit with a driver (W#1) by an average hitter. The initial velocity value in this case is the same as that of the device and conditions used to measure the initial velocity of the core and each covered sphere described above.

[0088] [ Regarding the relationship between the initial velocities of each sphere 〕 In the present invention, the relationship between the initial velocity of the intermediate layer-covered sphere and the initial velocity of the ball is expressed by the following formula, from the viewpoint of achieving both advantageous flight distance when hit with a driver (W#1) by an average hitter and controllability during the short game. (Initial speed of ball)<(Initial speed of middle layer covered sphere) It is necessary to satisfy the above. The value obtained by subtracting the initial velocity of the ball from the initial velocity of the intermediate layer-covered sphere is greater than 0.0 m / s, preferably 0.10 m / s or more, more preferably 0.30 m / s or more, and the upper limit is preferably 1.00 m / s or less, more preferably 0.70 m / s or less, and even more preferably 0.50 m / s or less. If this value is too large, the amount of spin increases during full shots and the initial velocity of actual shots decreases, and the target distance may not be obtained when the average hitter hits with a driver (W#1). On the other hand, if this value is too small and this is due to the cover, the cover becomes hard and the amount of spin is reduced during short games, and the durability of repeated hits is poor. Also, if this value is too small and this is due to the intermediate layer, the amount of spin increases during full shots and the average hitter may not be able to obtain the target distance when hitting with a driver (W#1).

[0089] The value obtained by subtracting the initial velocity of the envelope layer-covered sphere from the initial velocity of the intermediate layer-covered sphere is preferably 0.10 m / s or more, more preferably 0.20 m / s or more, and even more preferably 0.30 m / s or more, with the upper limit being preferably 0.70 m / s or less, more preferably 0.60 m / s or less, and even more preferably 0.57 m / s or less. If this value is too large and is caused by the intermediate layer, the durability to cracking during repeated impacts may be poor. Also, if this value is large and is caused by the envelope layer, the amount of spin increases when a full shot is made, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1).

[0090] The initial velocity of the envelope-coated sphere minus the initial velocity of the core is preferably 0.20 m / s or more, more preferably 0.65 m / s or more, and even more preferably 0.80 m / s or more, with the upper limit being preferably 1.05 m / s or less, more preferably 1.00 m / s or less, and even more preferably 0.95 m / s or less. If this value is too large, the durability against cracking may deteriorate when repeatedly hit. If this value is too small, the amount of spin increases when a full shot is made, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1).

[0091] The value obtained by subtracting the initial velocity of the core from the initial velocity of the intermediate layer-covered sphere is preferably 1.00 m / s or more, more preferably 1.15 m / s or more, and even more preferably 1.30 m / s or more, with the upper limit being preferably 1.60 m / s or less, more preferably 1.55 m / s or less, and even more preferably 1.50 m / s or less. If this value is too large, the durability against cracking may deteriorate when repeatedly hit. If this value is too small, the amount of spin increases when a full shot is made, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1).

[0092] [ Core diameter and ball diameter 〕 The relationship between the core diameter and the ball diameter, i.e., the value of (core diameter) / (ball diameter) is preferably 0.820 or more, more preferably 0.824 or more, and even more preferably 0.828 or more. On the other hand, the upper limit is preferably 0.970 or less, more preferably 0.920 or less, and even more preferably 0.900 or less. If this value is too small, the initial velocity of the ball will be low, or the amount of deflection of the entire ball will be small, making the ball hard, and the spin rate of the ball will increase on a full shot, and the flight distance when hit with a driver (W#1) by an average hitter may be shorter than the target. On the other hand, if the above value is too large, the spin rate of the ball will increase on a full shot, and the flight distance when hit with a driver (W#1) by an average hitter may be shorter than the target, or the durability to cracking when hit repeatedly may be poor.

[0093] [ Relationship between surface hardness of each sphere 〕 The value obtained by subtracting the center hardness of the core from the surface hardness of the envelope-coated sphere is preferably 24 or more, more preferably 27 or more, and even more preferably 30 or more, with the upper limit being preferably 42 or less, more preferably 39 or less, and even more preferably 36 or less. If the above value is too large, the durability to cracking during repeated impacts may be poor, or the initial velocity of actual impact may be low, making it impossible for an average hitter to achieve the desired flight distance when hitting with a driver (W#1). If the above value is too small, the amount of spin of the ball increases during a full shot, making it impossible for an average hitter to achieve the desired flight distance when hitting with a driver (W#1).

[0094] The surface hardness of the envelope-coated sphere minus the surface hardness of the core is, in Shore C hardness, preferably greater than 0, more preferably at least 2, and even more preferably at least 4, with the upper limit being preferably not more than 25, more preferably not more than 15, and even more preferably not more than 10. If the value is outside the above range, the amount of spin on the ball increases on a full shot, and an average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1).

[0095] The surface hardness of the intermediate layer-covered sphere minus the center hardness of the core is preferably 35 or more, more preferably 38 or more, and even more preferably 40 or more, with the upper limit being preferably 52 or less, more preferably 48 or less, and even more preferably 45 or less. If the above value is too large, the durability to cracking during repeated impacts may be poor, or the initial velocity of actual impact may be low, making it difficult for an average hitter to achieve the desired flight distance when hitting with a driver (W#1). If the above value is too small, the amount of spin of the ball increases during a full shot, making it difficult for an average hitter to achieve the desired flight distance when hitting with a driver (W#1).

[0096] The surface hardness of the intermediate layer-coated sphere minus the surface hardness of the surrounding layer-coated sphere is preferably 1 or more, more preferably 3 or more, and even more preferably 5 or more, in Shore C hardness, with the upper limit being preferably 25 or less, more preferably 17 or less, and even more preferably 14 or less. If the above value is outside the above range, the amount of spin on the ball increases on a full shot, and an average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1).

[0097] The value obtained by subtracting the surface hardness of the ball from the surface hardness of the intermediate layer-covered sphere is preferably 2 or more, more preferably 4 or more, and even more preferably 6 or more in Shore C hardness, with the upper limit being preferably 25 or less, more preferably 17 or less, and even more preferably 14 or less. If the value is too small, controllability in the short game may deteriorate. If the value is too large, the amount of spin on a full shot increases, and an average hitter may not be able to achieve the desired distance when hitting with a driver (W#1).

[0098] [ Specific gravity relationship between the middle layer and the cover 〕 It is recommended that the difference between the specific gravity of the cover and that of the intermediate layer be within ±0.15, preferably within ±0.10, and more preferably within ±0.05. In other words, if the difference in specific gravity is too large, and the intermediate layer material and / or the cover material cannot be molded completely concentrically with these layers and the layer located inside, and become eccentric, the ball may deviate significantly from side to side when hit with a putter.

[0099] A large number of dimples may be formed on the outer surface of the cover. There are no particular limitations on the number of dimples to be 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 is outside the above range, the average hitter may experience a short flight distance when hitting with a driver (W#1).

[0100] The shape of the dimples may be one or a combination of two or more of the following shapes: circular, various polygonal, dewdrop, elliptical, etc. For example, when using circular dimples, the diameter may be about 2.5 mm to 6.5 mm, and the depth may be 0.08 mm to 0.30 mm.

[0101] The dimple occupancy rate 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 spherical area assuming no dimples (SR value), is preferably 75% or more, more preferably 80% or more, and even more preferably 84% or more, with an upper limit of 90% or less, more preferably 88% or less, and even more preferably 86% or less. If the SR value deviates from the above range, the flight distance when hit with a driver (W#1) by an average hitter may be reduced.

[0102] The VR value, which is the percentage of the total dimple volume formed below the plane surrounded by the dimple edges to the volume of the ball assuming that no dimples exist, is 0.79% or more, preferably 0.80% or more, more preferably 0.81% or more, with the upper limit being 0.89% or less, more preferably 0.88% or less, and more preferably 0.87% or less. If this VR value is greater than the above range, the distance traveled by a long hitter when hitting with a driver (W#1) may be too low, or the target distance may not be obtained when hitting with a driver (W#1) by an average hitter. In addition, in this case, the trajectory may be low, making it difficult to achieve a carry and making it difficult to cross valleys or ponds. On the other hand, if the above value is too small, the distance traveled by a long hitter when hitting with a driver (W#1) may not be reduced, and the ball may fly longer than the standard distance of the new distance rule envisaged by the R&A and the USGA.

[0103] The value V0, obtained by dividing the spatial volume of the dimple below the plane surrounded by the edge of each dimple by the volume of a cylinder whose bottom is the plane and whose height is the maximum depth of the dimple from the bottom, is preferably 0.35 or more, more preferably 0.38 or more, and even more preferably 0.40 or more, with the upper limit being 0.80 or less, more preferably 0.70 or less, and even more preferably 0.60 or less. If this V0 value deviates from the above range, the flight distance when hit with a driver (W#1) by long hitters and average hitters may be shorter than the target.

[0104] 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 218000 and a spin rate of 2800 rpm is A1, the ratio (CL2 / CD2) of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184000 and a spin rate of 2900 rpm is A2, and the ratio (CL3 / CD3) of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158000 and a spin rate of 3100 rpm is A3, the following two equations can be used to determine the ratio of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218000 and a spin rate of 2800 rpm: 0.590≦A1≦0.640, and (A2+A3) / 2≧0.670 The dimples are appropriately designed to satisfy the above.

[0105] In this specification, "lift coefficients (CL1, CL2, CL3) and drag coefficients (CD1, CD2, CD3)" are measured in accordance with the ITR (Indoor Test Range) defined by the USGA (United States Golf Association). The lift coefficient and drag coefficient can be adjusted by adjusting the configuration (arrangement, diameter, depth, volume, number, shape, etc.) of the dimples on the golf ball. 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 by the following formula (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.

[0106] 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.

[0107] Regarding the conditions for measuring the above lift coefficient CL1 and drag coefficient CD1, 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 long hitter hits the ball with a driver (W#1), this Reynolds number corresponds to the ball speed when a golf ball is hit with a head speed (HS) of 54 m / s, and the spin rate of 2,800 rpm corresponds to the average spin condition for a player with a head speed (HS) of 54 m / s.

[0108] Regarding the conditions for measuring the above 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 average hitter 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 the spin rate of 2,900 rpm is the average spin condition for a player with a head speed (HS) of 45 m / s.

[0109] Regarding the conditions for measuring the above 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 average hitter 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 the spin rate of 3,100 rpm is the average spin condition for a player with a head speed (HS) of 40 m / s.

[0110] The ratio of the lift coefficient CL1 to the drag coefficient CD1, i.e., the value of CL1 / CD1=A1, is 0.590 or more, preferably 0.595 or more, more preferably 0.600 or more, with the upper limit being 0.640 or less, preferably 0.634 or less, more preferably 0.627 or less. If this value is too large, the effect of suppressing the flight distance when a long hitter hits with a driver (W#1) is insufficient, and the flight distance may be too long. On the other hand, if the above value is too small, the actual flight distance may be too short compared to the target flight distance.

[0111] 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 more, more preferably 0.645 or more, and even more preferably 0.655 or more, with the upper limit being preferably 0.668 or less, more preferably 0.666 or less, and even more preferably 0.664 or less. When the value of A1 is 0.614 to 0.640, the value of A2 is preferably 0.669 or more, more preferably 0.671 or more, and even more preferably 0.673 or more, 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 above values ​​deviate from the above ranges, the ball may fly up or have a trajectory that does not produce a carry when hit by an average hitter with a driver (W#1), and the target total distance may not be obtained.

[0112] 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 more, more preferably 0.705 or more, and even more preferably 0.715 or more, with the upper limit being preferably 0.734 or less, more preferably 0.731 or less, and even more preferably 0.728 or less. When the value of A1 is 0.614 to 0.640, the value of A3 is preferably 0.735 or more, more preferably 0.738 or more, and even more preferably 0.741 or more, 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 above values ​​deviate from the above ranges, the ball may fly up or have a trajectory that does not produce a carry when hit by an average hitter with a driver (W#1), and the target total distance may not be obtained.

[0113] The average value 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, and the upper limit is 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, when an average hitter hits with a driver (W#1), the ball may not carry and the desired total distance may not be obtained. On the other hand, if the above value is too high, when an average hitter hits with a driver (W#1), the ball may fly up and the desired distance may not be obtained.

[0114] The multi-piece solid golf ball of the present invention can be made for competitive use in accordance with the Rules of Golf, 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. EXAMPLES

[0115] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. That is, the present invention can be implemented in many aspects, and should not be interpreted as being limited to the contents described in the embodiments. In addition, the numerical values ​​described in the following examples are merely examples, and the interpretation of the present invention is not limited thereto.

[0116] [Examples 1 to 4, Comparative Examples 1 to 9] Core formation For Examples 1 to 4 and Comparative Examples 1 to 9, the rubber compositions shown in Table 1 were prepared and vulcanized under the vulcanization conditions shown in Table 1 to produce solid cores.

[0117] [Table 1]

[0118] Details of the above formulation are as follows: Polybutadiene A: Product name "BR 01" (manufactured by ENEOS Materials) Polybutadiene B: Product name "BR 730" (manufactured by ENEOS Materials Co., Ltd.) Zinc acrylate: Product name "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.) Zinc methacrylate: Trade name "ZDA-90" (Asada Chemical Industry Co., Ltd.) Organic peroxide: Dicumyl peroxide, trade name "Percumyl D" (manufactured by NOF Corporation) Water: Pure water (Seiki Pharmaceutical Co., Ltd.) Anti-aging agent: 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.

[0119] Formation of the Enveloping Layer Next, for each Example and Comparative Example, an envelope layer is formed around the core by injection molding using envelope layer material having a composition of No. 1 shown in Table 2. In Comparative Examples 7 to 9, no envelope layer is formed.

[0120] Formation of the intermediate layer Next, an intermediate layer is formed around the surrounding layer-covered sphere obtained above by injection molding using intermediate layer materials having blends No. 3 to No. 6 shown in Table 2.

[0121] Formation of the cover (outermost layer) Next, a cover (outermost layer) is formed around the intermediate layer-covered sphere of each of the above examples by injection molding using cover materials having formulations No. 7 to No. 9 shown in Table 2.

[0122] [Table 2]

[0123] The details of the ingredients in Table 2 are as follows: "HPF1000" (trademark) "HPF" manufactured by The Dow Chemical Company "Himilan 1605", "Himilan 1557", "Himilan 1706", "AM7318" and "AM7327" are ionomers manufactured by Dow Mitsui Polychemicals. "Barium sulfate" "Precipitated Barium Sulfate 300" manufactured by Sakai Chemical Industry Co., Ltd. "Trimethylolpropane" (TMP) manufactured by Tokyo Chemical Industry Co., Ltd. "Hytrel 4001" Thermoplastic polyester elastomer manufactured by Toray Celanese "TPU (1)": Trade name "Pandex" manufactured by DIC Covestro Polymer, ether type thermoplastic polyurethane, material hardness (Shore D) "43" "TPU (2)": Trade name "Pandex" manufactured by DIC Covestro Polymer, ether type thermoplastic polyurethane, material hardness (Shore D) "50"

[0124] The dimples used in each of the examples and comparative examples were dimples (1) to (4) below. Each dimple pattern included eight types of circular dimples, No. 1 to No. 8, which differ in diameter and depth. Details are shown in Table 3 below. The arrangement (pattern) of dimples (1) to (4) is shown in Figure 5. Figure 5(A) shows a plan view of the dimples, and Figure 5(B) is a side view of the same.

[0125] [Table 3]

[0126] Definition of a Dimple Edge: The highest point on the cross section passing through the center of the dimple Diameter: The diameter of the plane enclosed by the edge of the dimple Depth: The maximum depth of the dimple from the plane bounded by the dimple edge SR: The ratio of the total dimple area, defined by the plane enclosed by the edges of the dimples, to the area of ​​the ball as if the dimples did not exist. Dimple volume: The volume of the dimple below the plane surrounded by the edge of the dimple 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 ratio of the total volume of the dimples formed below the plane surrounded by the edges of the dimples to the volume of the ball as if the dimples did not exist.

[0127] The following table shows the lift coefficient CL1, drag coefficient CD1, and ratio CL1 / CD1=A1 for a Reynolds number of 218000 and a spin rate of 2800 rpm, the lift coefficient CL2, drag coefficient CD2, and ratio CL2 / CD2=A2 for a Reynolds number of 184000 and a spin rate of 2900 rpm, and the lift coefficient CL3, drag coefficient CD3, and ratio CL3 / CD3=A3 for a Reynolds number of 158000 and a spin rate of 3100 rpm for a ball with the above dimples (1) to (4) formed on the cover surface. These lift coefficients and drag coefficients are measured in accordance with the ITR (Indoor Test Range) defined by the USGA.

[0128] [Table 4]

[0129] For each of the obtained 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 by the methods described below. The results are shown in Tables 5 to 8.

[0130] Core hardness distribution The surface of the core is spherical, and the needle of the hardness tester is set almost perpendicular to the spherical surface, and the surface hardness is measured in Shore C hardness according to ASTM D2240. For the center and specified positions of the core, the core is cut into a hemisphere to make the cross section flat, and the needle of the hardness tester is pressed perpendicularly against the center part and the specified positions shown in Tables 5 and 6 to measure the hardness, and the hardness at the center and each position is shown in Shore C hardness values. The hardness is measured using an automatic rubber hardness tester "P2" made by Kobunshi Keiki Co., Ltd., equipped with a Shore C type hardness tester. The hardness value is the maximum value. All measurements are performed in an environment of 23±2°C. The values ​​in the table are Shore C hardness values. In addition, in terms of the core hardness distribution, the Shore C hardness Cc at the center of the core, the Shore C hardness Cm at the midpoint M between the center and the surface of the core, the Shore C hardnesses at positions 2mm, 4mm, and 6mm inward from the midpoint M are Cm-2, Cm-4, and Cm-6, respectively, the Shore C hardnesses at positions 2mm, 4mm, and 6mm outward from the center M are Cm+2, Cm+4, and Cm+6, respectively, and the Shore C hardness Cs on the surface of the core is calculated based on 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) Calculate the values ​​of the following three formulas: (1)Area E+Area F (2)(Area E+Area F)-(Area A+Area B) (3)(Area D+Area E)-(Area B+Area C)

[0131] To illustrate 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 9 are shown in FIGS.

[0132] The outer diameter of each of the core, the surrounding layer-coated sphere, and the intermediate layer-coated sphere The temperature is regulated in a thermostatic chamber at 23.9±1°C for at least three hours, and then measurements are taken at five random points on the surface in a room at 23.9±2°C. The average of these measurements is used as the measurement value for each sphere, and the average value for 10 measurements is calculated.

[0133] Ball diameter The ball is placed in a thermostatic bath 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 taken as the measurement for one ball. The average of the 10 balls measured is then calculated.

[0134] Deflection of the core, the envelope layer covered sphere, the intermediate layer covered sphere, and the ball Each covered sphere is placed on a hard plate and the amount of deflection is measured when an initial load of 98N (10kgf) is applied and then a final load of 1275N (130kgf) is applied. Note that the above deflection amount is a value measured in a room at 23.9±2°C after controlling the temperature at 23.9±1°C for at least three hours. The measuring device used is a high-load compression tester manufactured by MU Seiki Co., Ltd., and the down speed of the pressure head compressing the core, each layer of covered sphere, or the ball is 10mm / s.

[0135] Material hardness of the envelope layer, intermediate layer and cover (Shore C hardness, Shore D hardness) The resin material for each layer is formed into a sheet 2 mm thick and left at a temperature of 23±2°C for two weeks. Three sheets are stacked when measuring. Shore C hardness and Shore D hardness are measured using a Shore C hardness tester and a Shore D hardness tester 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 type hardness tester or a Shore D type hardness tester is used. The hardness value is read as the maximum value. The measurement method follows the ASTM D2240 standard.

[0136] 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 areas 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 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 type hardness tester or a Shore D type hardness tester is used. The hardness value is read as the maximum value. The measurement method complies with the ASTM D2240 standard.

[0137] The initial velocity of each sphere 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 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 shot at four different entry velocities at each air pressure, and the ball is allowed to collide with the barrier, and its COR (coefficient of restitution) is measured. In other words, the air pressure is changed to four levels, and a correlation equation between the entry velocity and COR is created. Similarly, a correlation equation between the entry velocity and contact time is created. 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 equation 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).) In measuring the initial velocity of each sphere, the barrel diameter is selected so that the clearance between the outer diameter of the measured object and the barrel diameter on one side is between 0.2 and 2.0 mm. For the core, a barrel diameter of 38.23 mm is selected for Examples 1 to 4 and Comparative Examples 1 to 5, 36.58 mm for Comparative Example 6, and 39.88 mm for Comparative Examples 7 to 9. For the envelope layer covered spheres, a barrel diameter of 39.88 mm is selected for all examples, for the intermediate layer covered spheres, a barrel diameter of 41.53 mm is selected for all examples, and for the balls, a barrel diameter of 43.18 mm is selected for all examples.

[0138] [Table 5]

[0139] [Table 6]

[0140] [Table 7]

[0141] [Table 8]

[0142] The flight distance (W#1), controllability during approach and durability upon impact of each golf ball were evaluated by the following methods. The results are shown in Table 9.

[0143] Flight rating (W#1, HS54m / s) A driver club is attached to the golf hitting robot, and the spin rate and flight distance (total) 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 (2016 model) (loft angle 8.5°), and the evaluation is based on the following criteria. 〔Judgment criteria〕 ◯: The total compared to Comparative Example 8 is −7.0 m or less and −20.0 m or more. Δ: The total compared to Comparative Example 8 is less than −20.0 m. × The total compared to Comparative Example 8 is greater than -7.0 m.

[0144] Flight rating (W#1, HS45m / s) A driver club is attached to the golf hitting robot, and the spin rate and flight distance (total) are measured when hitting the ball at a head speed (HS) of 45 m / s. The club used is the Bridgestone Sports JGR Driver (2016 model) (loft angle 9.5°), and is evaluated according to the following criteria. 〔Judgment criteria〕 ◯: The total compared to Comparative Example 8 is -5.0 m or more. Δ: The total compared to Comparative Example 8 is equal to or greater than -10.0 m and less than -5.0 m. × The total compared to Comparative Example 8 is less than −10.0 m.

[0145] Flight rating (W#1, HS40m / s) A driver club is attached to the golf hitting robot, and the spin rate and flight distance (total) are measured when hitting the ball at a head speed (HS) of 40 m / s. The club used is the Bridgestone Sports JGR Driver (2016 model) (loft angle 9.5°), and is evaluated according to the following criteria. 〔Judgment criteria〕 ◯: The total compared to Comparative Example 8 is +1.0 m or more. Δ: The total compared to Comparative Example 8 is equal to or greater than −4.0 m and less than +1.0 m. × The total compared to Comparative Example 8 is less than −4.0 m.

[0146] Evaluation of spin rate during approach (SW, HS15m / s) The amount of spin is judged by hitting the ball with a golf hitting robot equipped with a sand wedge at a head speed (HS) of 15 m / s. The amount of spin is measured by using an initial condition measuring device to measure the ball immediately after hitting it. The sand wedge used is the Bridgestone Sports TourStage TW-03 (loft angle 57°) 2002 model. 〔Judgment criteria〕 〇 ··· Spin rate 4500 rpm or more × Spin rate less than 4500 rpm

[0147] Repeated impact durability The durability of the ball is evaluated using the ADC Ball COR Durability Tester manufactured by Automated Design Corporation in the United States. This test machine has the function of launching a golf ball with air pressure and then colliding it continuously with two metal plates placed in parallel. The incidence speed on the metal plates is set to 43 m / s. The number of times it is shot until the golf ball breaks is measured, and the average value of the measurements for 10 golf balls is calculated. This average value is evaluated according to the following criteria. 〔Judgment criteria〕 〇 181 or more times × 180 times or less

[0148] [Table 9]

[0149] As shown in the results in Table 9, the golf balls of Comparative Examples 1 to 9 are inferior to the products of the present invention (Examples) in the following respects. In Comparative Example 1, the A1 value was greater than 0.655, and the flight distance was too long when using a driver (W#1) at a head speed (HS) of 54 m / s. In Comparative Example 2, the A1 value is smaller than 0.590, and the (A2+A3) / 2 value is smaller than 0.670. The flight distance at a head speed (HS) of 54 m / s with a driver (W#1) is too low, and the flight distance at a head speed (HS) of 45 m / s with a driver (W#1) is also poor. In Comparative Example 3, the amount of deflection of the ball was greater than 3.0 mm, and the durability against repeated impacts was inferior to the respective Examples. In Comparative Example 4, the amount of deflection of the ball was greater than 3.0 mm, and the durability against repeated impacts was inferior to the respective Examples. In Comparative Example 5, the amount of deflection of the ball was greater than 3.0 mm, and the durability against repeated impacts was inferior to the respective Examples. In Comparative Example 6, the ball deflection was greater than 3.0 mm, the initial velocity of the ball was greater than the initial velocity of the intermediate layer-covered sphere, the spin rate on approach was reduced, and the durability to repeated hits was poor. Comparative Example 7 is a ball having a three-piece structure with no surrounding layer, and is inferior to the respective Examples in durability against repeated impacts. Comparative Example 8 is the first embodiment of a tour ball used by professionals and advanced players. It has a three-piece structure without an envelope layer, the A1 value is greater than 0.655, and the ball achieves too much distance when used with a driver (W#1) at a head speed (HS) of 54 m / s. Comparative Example 9 is a second embodiment of a tour ball used by professionals and advanced players. It has a three-piece structure without an envelope layer, the A1 value is greater than 0.655, and the ball achieves too much distance when used with a driver (W#1) at a head speed (HS) of 54 m / s. [Explanation of symbols]

[0150] G Golf ball 1 core 2. Enclosure Layer 3. Middle tier 4 Cover D dimple

Claims

1. A multi-piece solid golf ball comprising a core, an envelope layer, an intermediate layer and a cover, and a number of dimples formed on the outer surface of the cover, wherein the core is formed of a single layer or multiple layers of a rubber composition, the envelope layer is formed of a single layer or multiple layers of a resin composition, and the intermediate layer and the cover are both formed of a single layer of a resin composition, and the relationship between the initial velocity of the intermediate layer-covered sphere and the initial velocity of the ball is expressed by the following formula: (Initial velocity of ball) < (Initial velocity of intermediate layer-coated sphere) and the amount of deflection when the ball is subjected to an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is 3.0mm or less, and 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 2,800rpm 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 2,900rpm 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 3,100rpm is A3, the following two equations are satisfied: 0.590≦A1≦0.640, and (A2+A3) / 2≧0.670 A multi-piece solid golf ball comprising:

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. 3. The multi-piece solid golf ball according to claim 2, wherein the value of A1 is 0.614 to 0.640, 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. The following three formulas: (Initial velocity of intermediate layer-coated sphere)−(Initial velocity of surrounding layer-coated sphere)≦0.70 (m / s) (Initial velocity of the envelope-coated sphere)−(Initial velocity of the core)≧0.20 (m / s) 1.00≦(initial velocity of intermediate layer-coated sphere)−(initial velocity of core)≦1.60 (m / s) 3. The multi-piece solid golf ball according to claim 1, wherein the above-mentioned formula (1) is satisfied.

6. The following formula, 0.65≦(initial velocity of the envelope layer-coated sphere)−(initial velocity of the core)≦1.00 (m / s) 3. The multi-piece solid golf ball according to claim 1, wherein the above-mentioned formula (1) is satisfied.

7. The following formula, Ball surface hardness <Surface hardness of intermediate layer covered sphere> Surface hardness of envelope layer covered sphere> Core surface hardness (Note that the surface hardness of each sphere mentioned above means Shore C hardness.) 3. The multi-piece solid golf ball according to claim 1, wherein the above-mentioned formula (1) is satisfied.

8. 3. The multi-piece solid golf ball according to claim 1, wherein the intermediate layer contains an inorganic granular filler and the specific gravity of the resin material of the intermediate layer is 1.05 or more.

9. 3. The multi-piece solid golf ball according to claim 1, wherein the difference between the specific gravity of the cover and the specific gravity of the intermediate layer is within 0.

15.

10. 3. The multi-piece solid golf ball according to claim 1, wherein the resin composition of the intermediate layer contains a high-acid ionomer resin having an acid content of 16% by mass or more.

11. The following formula, Cover thickness < Intermediate layer thickness ≦ Enveloping layer thickness 3. The multi-piece solid golf ball according to claim 1, wherein the above-mentioned formula (1) is satisfied.

12. In the hardness distribution of the above 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 center 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 as follows: ・Area A: 1 / 2 x 2 x (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 / 2×2×(Cm+4-Cm+2) ・Area F: 1 / 2 x 2 x (Cm+6-Cm+4) Regarding (Area E + Area F) - (Area A + Area B) ≧1.0 3. The multi-piece solid golf ball according to claim 1, wherein the above-mentioned formula (1) is satisfied.

13. The following formula, 35≦(surface hardness of intermediate layer-coated sphere)−(center hardness of core) (However, hardness refers to Shore C hardness.) 8. The multi-piece solid golf ball according to claim 7, which satisfies the above.

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