Golf Ball

Abstract

A golf ball 2 includes a core 4, an inner cover 6 positioned outside the core 4, and an outer cover 8 positioned outside the inner cover 6. The core 4 has a capsule 14, a plurality of separators 16, an electronic unit 18, and a plurality of fillings 20. The capsule 14 has a melting point of not lower than 100.degree. C. A ratio P1 of a volume Vr of the capsule 14 to a volume Vc of the core 4 is not less than 25% and not greater than 75%. The electronic unit 18 is housed in the capsule 14. The electronic unit 18 detects behavior of the golf ball 2.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority on and the benefit of Patent Application No. 2020-185904 filed in JAPAN on Nov. 6, 2020 and Patent Application No. 2020-186684 filed in JAPAN on Nov. 9, 2020. The entire disclosures of these Japanese Patent Applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] The present invention relates to golf balls. Specifically, the present invention relates to golf balls including an electronic unit for measuring behavior thereof.

Description of the Related Art

[0003] A golf ball is launched by being hit with a golf club. The speed of the golf ball immediately after the hit is referred to as "initial speed". With a golf ball having excellent resilience performance, a high initial speed is achieved. A high initial speed is advantageous in flight distance.

[0004] The face of a golf club has a loft angle. When a golf ball is hit with the golf club, the golf ball is launched at a launch angle corresponding to the loft angle. Furthermore, in the golf ball, backspin due to the loft angle occurs. The golf ball flies with the backspin. The backspin produces a displacement between the separation point on the upper side and the separation point on the lower side of the air around the golf ball. Due to the displacement, lift force acts on the golf ball. The launch angle and the backspin rate affect the trajectory of the golf ball.

[0005] If the rate of backspin is high at the time of landing, the run of the golf ball is small. When a golf ball having a high backspin rate is used, a golf player can cause the golf ball to stop at a target point. If the rate of backspin is low at the time of landing, the run of the golf ball is large. When a golf ball having a low backspin rate is used, a golf player can obtain a large flight distance.

[0006] Due to the intention of a golf player, sidespin may occur in a golf ball. If the rate of the sidespin is high, the golf ball tends to curve. When a golf ball with which a high sidespin rate can be achieved is used, a golf player can intentionally cause the golf ball to curve. Sidespin may occur against the intention of the golf player. The unintended sidespin causes an unintended golf ball trajectory.

[0007] When a golf ball is hit with a golf club, a shock occurs in the golf ball. The degree of the shock affects feel at impact. Golf players do not prefer excessive shocks.

[0008] When a golf ball is hit with a putter, the golf ball rolls with spin. This spin is generally overspin, but may be accompanied by some sidespin. For golf players, the rotation direction of spin is important. For golf players, the direction of travel of a golf ball immediately after being hit with a putter is also important.

[0009] The measurement of the behavior of a golf ball when being hit with a golf club or after the hit is important for trajectory analysis of the golf ball. This measurement is important in evaluating the skill of the golf player. Furthermore, this measurement is important in evaluating the golf club.

[0010] JP2019-042502 discloses a ball having a capsule including an electronic unit. The behavior of the ball can be measured by the electronic unit.

[0011] For trajectory analysis of a golf ball, evaluation of the skill of a golf player, and evaluation of a golf club, it is necessary to accurately measure the behavior of the golf ball. An object of the present invention is to provide a golf ball suitable for trajectory analysis or evaluation of golf equipment.

SUMMARY OF THE INVENTION

[0012] A golf ball according to the present invention includes a core and one or more covers positioned outside the core. The core has an electronic unit for detecting behavior of the golf ball and a capsule in which the electronic unit is housed and which has a melting point of not lower than 100.degree. C. A ratio P1 of a volume Vr of the capsule to a volume Vc of the core is not less than 25% and not greater than 75%.

[0013] In the golf ball, the size of the capsule is appropriate. Accurate measurement can be repeatedly performed by the golf ball.

[0014] Preferably, the core has, in the capsule, a positioning mechanism capable of fixing a position of the electronic unit with respect to the capsule by attaching the electronic unit. Preferably, the positioning mechanism is a separator fixed to the capsule and partitioning an inside of the capsule.

[0015] Preferably, the core has a filling positioned between the capsule and the electronic unit. Preferably, a base material of the filling is an epoxy resin. Preferably, the filling includes a matrix and a specific gravity adjusting agent dispersed in the matrix and having a density higher than a density of the matrix. Preferably, the specific gravity adjusting agent is tungsten powder.

[0016] Preferably, the capsule has a Shore D hardness of not less than 30.

[0017] A material of the capsule may be a resin composition. Preferably, a base resin of the resin composition is polycarbonate or polyether ether ketone.

[0018] In the golf ball, the one or more covers may include a cover formed by crosslinking a rubber composition. Preferably, the rubber composition includes [0019] (1) a base rubber, [0020] (2) a co-crosslinking agent, and [0021] (3) a crosslinking initiator having a 1-minute half-life temperature of not higher than 170.degree. C.

[0022] In the golf ball, the one or more covers may include a cover whose material is a resin composition. Preferably, a base resin of the resin composition is an ionomer resin or a polyurethane.

[0023] Preferably, in the golf ball, the one or more covers include an inner cover positioned outside the core and an outer cover positioned outside the inner cover. The inner cover is formed by crosslinking a rubber composition. A material of the outer cover is a resin composition. Preferably, the inner cover has a thickness of not less than 1.0 mm, the inner cover has a Shore D hardness of not greater than 50, the outer cover has a thickness of not less than 1.0 mm, and the outer cover has a Shore D hardness of not greater than 50.

[0024] According to another aspect, a golf ball according to the present invention includes a core and one or more covers positioned outside the core. The core has an electronic unit for detecting behavior of the golf ball. Any one of the one or more covers has a first hemisphere shell and a second hemisphere shell having a color different from a color of the first hemisphere shell.

[0025] In measurement using the golf ball, an appropriate hitting position can be easily selected. Accurate measurement can be made by the golf ball.

[0026] The electronic unit may have a sensor. Preferably, an angle of a straight line connecting a center of a circle forming a boundary between the first hemisphere shell and the second hemisphere shell and a center of gravity of the sensor, to the circle, is not less than 70.degree. and not greater than 90.degree..

[0027] Preferably, the core has a capsule having a melting point of not lower than 100.degree. C., and the electronic unit is housed in the capsule. Preferably, a ratio P1 of a volume Vr of the capsule to a volume Vc of the core is not less than 25% and not greater than 75%.

[0028] Preferably, the core has, in the capsule, a positioning mechanism capable of fixing a position of the electronic unit with respect to the capsule by attaching the electronic unit. Preferably, the positioning mechanism is a separator fixed to the capsule and partitioning an inside of the capsule.

[0029] Preferably, the core has a filling positioned between the capsule and the electronic unit.

[0030] A material of the capsule may be a resin composition.

[0031] Preferably, a base resin of the resin composition is polycarbonate or polyether ether ketone.

[0032] Preferably, in the golf ball, the one or more covers include an inner cover positioned outside the core and an outer cover positioned outside the inner cover. The inner cover is formed by crosslinking a rubber composition. The outer cover has the first hemisphere shell and the second hemisphere shell. A material of the first hemisphere shell is a resin composition. A material of the second hemisphere shell is a resin composition different from the resin composition of the first hemisphere shell.

[0033] Preferably, the rubber composition of the inner cover includes [0034] (1) a base rubber, [0035] (2) a co-crosslinking agent, and [0036] (3) a crosslinking initiator having a 1-minute half-life temperature of not higher than 170.degree. C.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 is a front view of a golf ball according to an embodiment of the present invention.

[0038] FIG. 2 is a schematic cross-sectional view of the golf ball in FIG. 1.

[0039] FIG. 3 is a front view of a golf ball according to another embodiment of the present invention.

[0040] FIG. 4 is a plan view of the golf ball in FIG. 3.

[0041] FIG. 5 is a schematic cross-sectional view taken along a line V-V in FIG. 4.

[0042] FIG. 6A is a plan view of the golf ball in FIG. 3 with a golf club head.

[0043] FIG. 6B is a front view of the golf ball and the golf club head in FIG. 6A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] The following will describe in detail the present invention based on preferred embodiments with appropriate reference to the drawings.

First Embodiment

[0045] A golf ball 2 shown in FIGS. 1 and 2 includes a core 4, an inner cover 6 positioned outside the core 4, and an outer cover 8 positioned outside the inner cover 6. The golf ball 2 has a plurality of dimples 10 on the surface thereof. Of the surface of the golf ball 2, a part other than the dimples 10 is a land 12. The golf ball 2 includes a paint layer and a mark layer on the external side of the outer cover 8, but these layers are not shown in the drawing.

[0046] The golf ball 2 has two covers. The number of covers may be 1. The number of covers may be 3 or more. The golf ball 2 may have another cover between the core 4 and the inner cover 6. The golf ball 2 may have another cover between the inner cover 6 and the outer cover 8. The golf ball 2 may have another cover on the external side of the outer cover 8.

[0047] The golf ball 2 preferably has a diameter of not less than 40 mm and not greater than 45 mm. From the viewpoint of conformity to the rules established by the United States Golf Association (USDA), the diameter is particularly preferably not less than 42.67 mm. In light of suppression of air resistance, the diameter is more preferably not greater than 44 mm and particularly preferably not greater than 42.80 mm.

[0048] The golf ball 2 preferably has a weight of not less than 40 g and not greater than 50 g. In light of attainment of great inertia, the weight is more preferably not less than 44 g and particularly preferably not less than 45.00 g. From the viewpoint of conformity to the rules established by the USGA, the weight is particularly preferably not greater than 45.93 g.

[0049] The core 4 is spherical. The core 4 has a capsule 14, a plurality of separators 16, an electronic unit 18, and a plurality of fillings 20.

[0050] The capsule 14 is spherical. The capsule 14 is hollow. Therefore, the capsule 14 has an internal space. A typical material for the capsule 14 is a resin composition. In the present embodiment, the capsule 14 is transparent.

[0051] FIG. 2 shows four separators 16. Each separator 16 generally has an "L" shape. The separator 16 has a pin 22 or a hole 24. The separator 16 is integrally formed with the capsule 14. Therefore, the material of the separator 16 is the same as that of the capsule 14. A separator 16 formed separately from the capsule 14 may be joined to the capsule 14. The material of the separator 16 may be different from that of the capsule 14. The separator 16 partitions the inside of the capsule 14. These separators 16 form a chamber 26 inside the capsule 14.

[0052] The electronic unit 18 is housed in the capsule 14. Specifically, the electronic unit 18 is housed in the chamber 26. Each separator 16 is in contact with the electronic unit 18. This contact prevents the electronic unit 18 from moving. In other words, the separator 16 fixes the position of the electronic unit 18 with respect to the capsule 14. The separator 16 is a positioning mechanism. The core 4 may have a positioning mechanism other than the separators 16. Positioning mechanisms having various shapes can be adopted. Positioning mechanisms made of various materials can be adopted.

[0053] The electronic unit 18 can detect the behavior of the golf ball 2. Specifically, the electronic unit 18 can detect a speed, a flight angle, a spin rate, a spin rotation axis direction, or a shock of the golf ball 2. The electronic unit 18 typically has a sensor, a control device, and a communication device. The sensor is typically an acceleration sensor. The acceleration sensor is disposed so as to be displaced from the center of gravity of the golf ball 2. The acceleration sensor performs detection on the basis of centrifugal force applied to the golf ball 2. The control device includes a CPU, a RAM, a ROM, and a battery. The control device receives a signal from the sensor and stores the signal in the RAM or the ROM. The CPU adds an operation to the signal from the sensor as necessary. The communication device transmits the signal obtained from the control device, to a device outside the golf ball 2.

[0054] The electronic unit 18 may have a light emitting device. The light emitting device can be turned on by a shock at the time of hitting. The light emitting device may be turned on by remote operation. The electronic unit 18 may have a speaker. The speaker can emit a sound by a shock at the time of hitting. The speaker may emit a sound by remote operation.

[0055] Each filling 20 is positioned between the capsule 14 and the electronic unit 18. The filling 20 is in contact with the inner peripheral surface of the capsule 14 and the electronic unit 18. The filling 20 can suppress a positional displacement of the electronic unit 18. The filling 20 can also absorb a shock transmitted to the electronic unit 18.

[0056] A typical material for the filling 20 is a resin composition. A typical base resin for the resin composition is an epoxy resin. The resin composition can contain a specific gravity adjusting agent.

[0057] Inside the capsule 14, there are vacant spaces 28. The electronic unit 18, the separators 16, the fillings 20, etc., do not exist in the vacant spaces 28. The golf ball 2 may include a core 4 having no vacant space 28. In the core 4 having no vacant space 28, all the portions of the inside of the capsule 14 other than the electronic unit 18 and the separators 16 are filled with the fillings 20.

[0058] As shown in FIG. 2, the inner cover 6 is positioned outside the core 4. The inner cover 6 surrounds the core 4. The inner cover 6 is formed by crosslinking a rubber composition. Examples of preferable base rubbers for use in the rubber composition include polybutadienes, polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-diene copolymers, and natural rubbers. In light of resilience performance of the golf ball 2, polybutadienes are preferable. When a polybutadiene and another rubber are used in combination, it is preferred if the polybutadiene is a principal component. Specifically, the proportion of the polybutadiene to the entire base rubber is preferably not less than 50% by weight and particularly preferably not less than 80% by weight. A polybutadiene in which the proportion of cis-1,4 bonds is not less than 80% is particularly preferable.

[0059] The rubber composition of the inner cover 6 preferably includes a co-crosslinking agent. Preferable co-crosslinking agents in light of durability and resilience performance of the golf ball 2 are monovalent or bivalent metal salts of an .alpha.,.beta.-unsaturated carboxylic acid having 2 to 8 carbon atoms. Examples of preferable co-crosslinking agents include zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate. Zinc acrylate and zinc methacrylate are particularly preferable.

[0060] The rubber composition may include a metal oxide and an .alpha.,.beta.-unsaturated carboxylic acid having 2 to 8 carbon atoms. They both react with each other in the rubber composition to obtain a salt. The salt serves as a co-crosslinking agent. Examples of preferable .alpha.,.beta.-unsaturated carboxylic acids include acrylic acid and methacrylic acid. Examples of preferable metal oxides include zinc oxide and magnesium oxide.

[0061] The amount of the co-crosslinking agent per 100 parts by weight of the base rubber is preferably not less than 10 parts by weight and not greater than 45 parts by weight. The golf ball 2 in which this amount is not less than 10 parts by weight has excellent resilience performance. From this viewpoint, this amount is more preferably not less than 15 parts by weight and particularly preferably not less than 20 parts by weight. The golf ball 2 in which this amount is not greater than 45 parts by weight has excellent feel at impact. From this viewpoint, this amount is more preferably not greater than 40 parts by weight and particularly preferably not greater than 35 parts by weight.

[0062] Preferably, the rubber composition of the inner cover 6 includes an organic peroxide. The organic peroxide serves as a crosslinking initiator. The organic peroxide contributes to the durability and the resilience performance of the golf ball 2. Examples of suitable organic peroxides include 1,1-di(t-butylperoxy)cyclohexane, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Two or more organic peroxides may be used in combination.

[0063] The amount of the organic peroxide per 100 parts by weight of the base rubber is preferably not less than 0.1 parts by weight and not greater than 3.5 parts by weight. The golf ball 2 in which this amount is not less than 0.1 parts by weight has excellent resilience performance. From this viewpoint, this amount is more preferably not less than 0.3 parts by weight and particularly preferably not less than 0.5 parts by weight. The golf ball 2 in which this amount is not greater than 3.5 parts by weight has excellent feel at impact. From this viewpoint, this amount is more preferably not greater than 3.0 parts by weight and particularly preferably not greater than 2.5 parts by weight.

[0064] Preferably, the rubber composition of the inner cover 6 includes an organic sulfur compound. The organic sulfur compound contributes to flight distance upon a shot with a driver. Organic sulfur compounds include naphthalenethiol compounds, benzenethiol compounds, and disulfide compounds.

[0065] Examples of naphthalenethiol compounds include 1-naphthalenethiol, 2-naphthalenethiol, 4-chloro-1-naphthalenethiol, 4-bromo-1-naphthalenethiol, 1-chloro-2-naphthalenethiol, 1-bromo-2-naphthalenethiol, 1-fluoro-2-naphthalenethiol, 1-cyano-2-naphthalenethiol, and 1-acetyl-2-naphthalenethiol.

[0066] Examples of benzenethiol compounds include benzenethiol, 4-chlorobenzenethiol, 3-chlorobenzenethiol, 4-bromobenzenethiol, 3-bromobenzenethiol, 4-fluorobenzenethiol, 4-iodobenzenethiol, 2,5-dichlorobenzenethiol, 3,5-dichlorobenzenethiol, 2,6-dichlorobenzenethiol, 2,5-dibromobenzenethiol, 3,5-dibromobenzenethiol, 2-chloro-5-bromobenzenethiol, 2,4,6-trichlorobenzenethiol, 2,3,4,5,6-pentachlorobenzenethiol, 2,3,4,5,6-pentafluorobenzenethiol, 4-cyanobenzenethiol, 2-cyanobenzenethiol, 4-nitrobenzenethiol, and 2-nitrobenzenethiol.

[0067] Examples of disulfide compounds include diphenyl disulfide, bis(4-chlorophenyl)disulfide, bis(3-chlorophenyl)disulfide, bis(4-bromophenyl)disulfide, bis(3-bromophenyl)disulfide, bis(4-fluorophenyl)disulfide, bis(4-iodophenyl)disulfide, bis(4-cyanophenyl)disulfide, bis(2,5-dichlorophenyl)disulfide, bis(3,5-dichlorophenyl)disulfide, bis(2,6-dichlorophenyl)disulfide, bis(2,5-dibromophenyl)disulfide, bis(3,5-dibromophenyl)disulfide, bis(2-chloro-5-bromophenyl)disulfide, bis(2-cyano-5-bromophenyl)disulfide, bis(2,4,6-trichlorophenyl)disulfide, bis(2-cyano-4-chloro-6-bromophenyl)disulfide, bis(2,3,5,6-tetrachlorophenyl)disulfide, bis(2,3,4,5,6-pentachlorophenyl)disulfide, and bis(2,3,4,5,6-pentabromophenyl)disulfide.

[0068] The amount of the organic sulfur compound per 100 parts by weight of the base rubber is preferably not less than 0.1 parts by weight and not greater than 1.5 parts by weight. The golf ball 2 in which this amount is not less than 0.1 parts by weight has excellent resilience performance. From this viewpoint, this amount is more preferably not less than 0.2 parts by weight and particularly preferably not less than 0.3 parts by weight. The golf ball 2 in which this amount is not greater than 1.5 parts by weight has excellent feel at impact. From this viewpoint, this amount is more preferably not greater than 1.0 part by weight and particularly preferably not greater than 0.8 parts by weight. Two or more organic sulfur compounds may be used in combination.

[0069] The rubber composition of the inner cover 6 may include a specific gravity adjusting agent. Examples of suitable specific gravity adjusting agents include zinc oxide, barium sulfate, calcium carbonate, and magnesium carbonate. The amount of the specific gravity adjusting agent is determined as appropriate so that the intended specific gravity of the inner cover 6 is achieved.

[0070] The rubber composition of the inner cover 6 may include additives, such as sulfur, a carboxylic acid, a carboxylate, an anti-aging agent, a coloring agent, a plasticizer, a dispersant, and the like, in an adequate amount. The rubber composition may include crosslinked rubber powder or synthetic resin powder.

[0071] The inner cover 6 preferably has a thickness of not less than 1.0 mm and not greater than 10.0 mm. The inner cover 6 having a thickness of not less than 1.0 mm can contribute to the resilience performance of the golf ball 2. From this viewpoint, the thickness is more preferably not less than 2.5 mm and particularly preferably not less than 3.5 mm. For the golf ball 2 in which the thickness is not greater than 10.0 mm, a sufficiently large capsule 14 can be adopted. From this viewpoint, the thickness is more preferably not greater than 8.0 mm and particularly preferably not greater than 7.5 mm.

[0072] The inner cover 6 preferably has a hardness of not less than 20 and not greater than 70. The golf ball 2 in which the hardness is not less than 20 has excellent resilience performance. From this viewpoint, the hardness is more preferably not less than 30 and particularly preferably not less than 35. The golf ball 2 in which the hardness is not greater than 70 has excellent feel at impact. From this viewpoint, the hardness is more preferably not greater than 60 and particularly preferably not greater than 50.

[0073] In measurement of the hardness of the inner cover 6, a Shore D type hardness scale is pressed against the surface of the inner cover 6. The temperature at the time of measurement is 23.degree. C.

[0074] The material of the inner cover 6 may be a resin composition. Examples of preferable base polymers for use in the resin composition include ionomer resins, polyurethanes, styrene block-containing thermoplastic elastomers, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, and thermoplastic polyolefin elastomers.

[0075] Ionomer resins are particularly preferable. Ionomer resins are highly elastic. The golf ball 2 that includes the inner cover 6 including an ionomer resin has excellent resilience performance. The golf ball 2 has excellent flight performance.

[0076] An ionomer resin and another resin may be used in combination. In this case, in light of resilience performance, the ionomer resin is included as the principal component of the base polymer. The proportion of the ionomer resin to the entire base polymer is preferably not less than 50% by weight.

[0077] Examples of preferable ionomer resins include binary copolymers formed with an .alpha.-olefin and an .alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon atoms. A preferable binary copolymer includes 80% by weight or more but 90% by weight or less of an .alpha.-olefin, and 10% by weight or more but 20% by weight or less of an .alpha.,.beta.-unsaturated carboxylic acid. The binary copolymer has excellent resilience performance. Examples of other preferable ionomer resins include ternary copolymers formed with: an .alpha.-olefin; an .alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon atoms; and an .alpha.,.beta.-unsaturated carboxylate ester having 2 to 22 carbon atoms. A preferable ternary copolymer includes 70% by weight or more but 85% by weight or less of an .alpha.-olefin, 5% by weight or more but 30% by weight or less of an .alpha.,.beta.-unsaturated carboxylic acid, and 1% by weight or more but 25% by weight or less of an .alpha.,.beta.-unsaturated carboxylate ester. The ternary copolymer has excellent resilience performance. For the binary copolymer and the ternary copolymer, preferable .alpha.-olefins are ethylene and propylene, while preferable .alpha.,.beta.-unsaturated carboxylic acids are acrylic acid and methacrylic acid. A particularly preferable ionomer resin is a copolymer formed with ethylene and acrylic acid. Another particularly preferable ionomer resin is a copolymer formed with ethylene and methacrylic acid.

[0078] In the binary copolymer and the ternary copolymer, some of the carboxyl groups are neutralized with metal ions. Examples of metal ions for use in neutralization include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions. The neutralization may be carried out with two or more types of metal ions. Particularly suitable metal ions in light of resilience performance and durability of the golf ball 2 are sodium ions, zinc ions, lithium ions, and magnesium ions.

[0079] Specific examples of ionomer resins include trade names "Himilan 1555", "Himilan 1557", "Himilan 1605", "Himilan 1706", "Himilan 1707", "Himilan 1856", "Himilan 1855", "Himilan AM7311", "Himilan AM7315", "Himilan AM7317", "Himilan AM7329", and "Himilan AM7337", manufactured by DOW-MITSUI POLYCHEMICALS CO., LTD.; trade names "Surlyn 6120", "Surlyn 6910", "Surlyn 7930", "Surlyn 7940", "Surlyn 8140", "Surlyn 8150", "Surlyn 8940", "Surlyn 8945", "Surlyn 9120", "Surlyn 9150", "Surlyn 9910", "Surlyn 9945", "Surlyn AD8546", "HPF1000", and "HPF2000", manufactured by E.I. du Pont de Nemours and Company; and trade names "IOTEK 7010", "IOTEK 7030", "IOTEK 7510", "IOTEK 7520", "IOTEK 8000", and "IOTEK 8030", manufactured by ExxonMobil Chemical Corporation. Two or more ionomer resins may be used in combination.

[0080] Preferably, the resin composition of the inner cover 6 includes a styrene block-containing thermoplastic elastomer together with an ionomer resin. The styrene block-containing thermoplastic elastomer includes a polystyrene block as a hard segment, and a soft segment. A typical soft segment is a diene block. Examples of compounds for the diene block include butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Butadiene and isoprene are preferable. Two or more compounds may be used in combination.

[0081] Examples of styrene block-containing thermoplastic elastomers include styrene-butadiene-styrene block copolymers (SBS), styrene-isoprene-styrene block copolymers (SIS), styrene-isoprene-butadiene-styrene block copolymers (SIBS), hydrogenated SBS, hydrogenated SIS, and hydrogenated SIBS. Examples of hydrogenated SBS include styrene-ethylene-butylene-styrene block copolymers (SEBS). Examples of hydrogenated SIS include styrene-ethylene-propylene-styrene block copolymers (SEPS). Examples of hydrogenated SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymers (SEEPS).

[0082] In light of resilience performance of the golf ball 2, the content of the styrene component in the styrene block-containing thermoplastic elastomer is preferably not less than 10% by weight, more preferably not less than 12% by weight, and particularly preferably not less than 15% by weight. In light of feel at impact of the golf ball 2, the content is preferably not greater than 50% by weight, more preferably not greater than 47% by weight, and particularly preferably not greater than 45% by weight.

[0083] In the present invention, styrene block-containing thermoplastic elastomers include an alloy of an olefin and one or more members selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS, and SEEPS. The olefin component in the alloy is presumed to contribute to improvement of compatibility with another base polymer. The alloy can contribute to the resilience performance of the golf ball 2. An olefin having 2 to 10 carbon atoms is preferable. Examples of suitable olefins include ethylene, propylene, butene, and pentene. Ethylene and propylene are particularly preferable.

[0084] Specific examples of polymer alloys include trade names "TEFABLOC T3221C", "TEFABLOC T3339C", "TEFABLOC SJ4400N", "TEFABLOC SJ5400N", "TEFABLOC SJ6400N", "TEFABLOC SJ7400N", "TEFABLOC SJ8400N", "TEFABLOC SJ9400N", and "TEFABLOC SR04", manufactured by Mitsubishi Chemical Corporation. Other specific examples of styrene block-containing thermoplastic elastomers include trade name "Epofriend A1010" manufactured by Daicel Corporation, and trade name "SEPTON HG-252" manufactured by Kuraray Co., Ltd.

[0085] In light of feel at impact, the proportion of the styrene block-containing thermoplastic elastomer to the entire base polymer is preferably not less than 10% by weight, more preferably not less than 15% by weight, and particularly preferably not less than 20% by weight. In light of resilience performance, this proportion is preferably not greater than 50% by weight.

[0086] The resin composition of the inner cover 6 may include a coloring agent, a specific gravity adjusting agent, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like in an adequate amount.

[0087] As shown in FIG. 2, the outer cover 8 is positioned outside the inner cover 6. The outer cover 8 surrounds the inner cover 6. The outer cover 8 is formed from a resin composition. Examples of preferable base polymers for use in the resin composition include ionomer resins, polyurethanes, styrene block-containing thermoplastic elastomers, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, and thermoplastic polyolefin elastomers.

[0088] Polyurethanes are particularly preferable. The outer cover 8 including a polyurethane can contribute to the spin performance of the golf ball 2. When a polyurethane and another resin are used in combination for the outer cover 8, the proportion of the polyurethane to the entire base resin is preferably not less than 50% by weight, more preferably not less than 60% by weight, and particularly preferably not less than 70% by weight.

[0089] The resin composition of the outer cover 8 may include a thermoplastic polyurethane or may include a thermosetting polyurethane. In light of productivity of the golf ball 2, the thermoplastic polyurethane is preferable. The thermoplastic polyurethane includes a polyurethane component as a hard segment, and a polyester component or a polyether component as a soft segment. The thermoplastic polyurethane is flexible. The outer cover 8 in which the polyurethane is used has excellent scuff resistance.

[0090] The thermoplastic polyurethane has a urethane bond within the molecule. The urethane bond can be formed by reacting a polyol with a polyisocyanate. The polyol, as a material for the urethane bond, has a plurality of hydroxyl groups. Low-molecular-weight polyols and high-molecular-weight polyols can be used.

[0091] Examples of low-molecular-weight polyols include diols, triols, tetraols, and hexaols. Specific examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, dipropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2,3-dimethyl-2,3-butanediol, neopentyl glycol, pentanediol, hexanediol, heptanediol, octanediol, and 1,6-cyclohexanedimethylol. Aniline diols or bisphenol A diols may be used. Specific examples of triols include glycerin, trimethylol propane, and hexanetriol. Specific examples of tetraols include pentaerythritol and sorbitol.

[0092] Examples of high-molecular-weight polyols include polyether polyols such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), and polytetramethylene ether glycol (PTMG); condensed polyester polyols such as polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexamethylene adipate (PHMA); lactone polyester polyols such as poly-.epsilon.-caprolactone (PCL); polycarbonate polyols such as polyhexamethylene carbonate; and acrylic polyols. Two or more polyols may be used in combination. In light of feel at impact of the golf ball 2, the high-molecular-weight polyol has a number average molecular weight of preferably not less than 400 and more preferably not less than 1000. The number average molecular weight is preferably not greater than 10000.

[0093] Examples of polyisocyanates, as a material for the urethane bond, include aromatic diisocyanates, alicyclic diisocyanates, and aliphatic diisocyanates. Two or more types of diisocyanates may be used in combination.

[0094] Examples of aromatic diisocyanates include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3'-bitolylene-4,4'-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), and paraphenylene diisocyanate (PPDI). One example of aliphatic diisocyanates is hexamethylene diisocyanate (HDI). Examples of alicyclic diisocyanates include 4,4'-dicyclohexylmethane diisocyanate (Hi.sub.2MDI), 1,3-bis(isocyanatomethyl)cyclohexane (H.sub.6XDI), isophorone diisocyanate (IPDI), and trans-1,4-cyclohexane diisocyanate (CHDI). 4,4'-dicyclohexylmethane diisocyanate is preferable.

[0095] Specific examples of the thermoplastic polyurethane include trade names "Elastollan NY80A", "Elastollan NY82A", "Elastollan NY83A", "Elastollan NY84A", "Elastollan NY85A", "Elastollan NY88A", "Elastollan NY90A", "Elastollan NY95A", "Elastollan NY97A", "Elastollan NY585", "Elastollan KP016N", and "Elastollan 1195A50STR", manufactured by BASF Japan Ltd.; and trade names "RESAMINE P4585LS" and "RESAMINE PS62490", manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.

[0096] The resin composition of the outer cover 8 may include a coloring agent, a filler, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like in an adequate amount. When the hue of the golf ball 2 is white, a typical coloring agent is titanium dioxide.

[0097] The outer cover 8 preferably has a thickness of not less than 0.3 mm and not greater than 3.0 mm. In the golf ball 2 in which the thickness is not less than 0.3 mm, the outer cover 8 can contribute to spin performance. From this viewpoint, the thickness is more preferably not less than 0.7 mm and particularly preferably not less than 1.0 mm. In the golf ball 2 in which the thickness is not greater than 3.0 mm, the outer cover 8 does not impair resilience performance. From this viewpoint, the thickness is more preferably not greater than 2.5 mm and particularly preferably not greater than 2.0 mm. The thickness is measured at a position immediately below the land 12.

[0098] The outer cover 8 preferably has a hardness of not less than 20 and not greater than 70. The golf ball 2 in which the hardness is not less than 20 has excellent resilience performance. From this viewpoint, the hardness is more preferably not less than 30 and particularly preferably not less than 35. The golf ball 2 in which the hardness is not greater than 70 has excellent feel at impact. From this viewpoint, the hardness is more preferably not greater than 60 and particularly preferably not greater than 50.

[0099] In measurement of the hardness of the outer cover 8, a Shore D type hardness scale is pressed against the surface of the outer cover 8. The temperature at the time of measurement is 23.degree. C.

[0100] The material of the outer cover 8 may be a resin composition containing a resin other than polyurethanes as a base material. The resin composition described above for the inner cover 6 can be used for the outer cover 8. The material of the outer cover 8 may be a crosslinked rubber composition.

[0101] The golf ball 2 may have a reinforcing layer between the inner cover 6 and the outer cover 8. The reinforcing layer firmly adheres to the inner cover 6 and also to the outer cover 8. The reinforcing layer suppresses separation of the outer cover 8 from the inner cover 6. The reinforcing layer is formed from a resin composition. Examples of a preferable base polymer of the reinforcing layer include two-component curing type epoxy resins and two-component curing type urethane resins. The reinforcing layer preferably has a thickness of not less than 5 .mu.m and not greater than 30 .mu.m.

[0102] The golf ball 2 may have a mid cover between the inner cover 6 and the outer cover 8. A preferable material for the mid cover is a resin composition. The resin described above as the base resin of the outer cover 8 can be used for the mid cover. In a preferable embodiment, the golf ball has an inner cover whose material is a crosslinked rubber composition, a mid cover whose base material is an ionomer resin, and an outer cover whose base material is a polyurethane.

[0103] When the golf ball 2 is hit with a golf club, the electronic unit 18 detects the behavior of the golf ball 2. The electronic unit 18 transmits a signal regarding the behavior to an external device. Trajectory analysis of the golf ball 2, evaluation of the skill of the golf player, and evaluation of the golf club can be performed on the basis of the signal.

[0104] A ratio P1 of a volume Vr of the capsule 14 to a volume Vc of the core 4 is preferably not less than 25% and not greater than 75%. The capsule 14 having a ratio P1 of not less than 25% has excellent durability. The golf ball 2 having the capsule 14 is less likely to break, even when being repeatedly hit. From this viewpoint, the ratio P1 is more preferably not less than 30% and particularly preferably not less than 35%. The golf ball 2 having the capsule 14 having a ratio P1 of not greater than 75% has excellent feel at impact. Therefore, a golf player can hit the golf ball 2 without hesitation. Due to this hit, the behavior of the golf ball 2 can be measured accurately. From this viewpoint, the ratio P1 is more preferably not greater than 73% and particularly preferably not greater than 70%.

[0105] The volume Vr of the capsule 14 is the volume of the material (resin composition) of the capsule 14. In the present embodiment, the capsule 14 is spherical.

[0106] Therefore, the volume Vr of the capsule 14 can be calculated by the following mathematical formulae.

Vr=4*.pi.*(R1.sup.3-R2.sup.3)/3

R1=D1/2

R2=D2/2

[0107] In these mathematical formulae, D1 represents the outer diameter of the capsule 14, and D2 represents the inner diameter of the capsule 14. In the present embodiment, the outer diameter of the core 4 is equal to the outer diameter D1 of the capsule 14. Therefore, the volume Vc of the core 4 can be calculated by the following mathematical formula.

Vc=4*.pi.*R1.sup.3/3

[0108] The outer diameter D1 of the capsule 14 is preferably not less than 25 mm and not greater than 35 mm. In the capsule 14 having an outer diameter D1 of not less than 25 mm, a sufficiently large electronic unit 18 can be housed. In the electronic unit 18, the sensor can be disposed at a position sufficiently away from the center of the golf ball 2. The capsule 14 can contribute to the accuracy of measurement. From this viewpoint, the outer diameter D1 is more preferably not less than 27 mm and particularly preferably not less than 28 mm. The golf ball 2 in which the outer diameter D1 is not greater than 35 mm is less likely to break, even when being repeatedly hit. Furthermore, the golf ball 2 can have performance close to that of a golf ball 2 including no electronic unit 18. From these viewpoints, the outer diameter D1 is more preferably not greater than 33 mm and particularly preferably not greater than 32 mm.

[0109] As described above, the material of the capsule 14 is a resin composition. The melting point of the capsule 14 (that is, the melting point of the resin composition) is preferably not lower than 100.degree. C. The capsule 14 having a melting point of not lower than 100.degree. C. is less likely to melt during formation of the cover. The capsule 14 can protect the electronic unit 18. From this viewpoint, the melting point is more preferably not lower than 110.degree. C. and particularly preferably not lower than 120.degree. C. The melting point is preferably not higher than 400.degree. C. The melting point of the base resin of the capsule 14 is preferably not lower than 100.degree. C., more preferably not lower than 110.degree. C., and particularly preferably not lower than 120.degree. C. The melting point of the base resin is preferably not higher than 400.degree. C.

[0110] In the present embodiment, the inner cover 6 directly covers the capsule 14. From the viewpoint of suppressing the melting of the capsule 14, the difference (T1-T2) between a melting point T1 of the capsule 14 and a molding temperature T2 of the cover that directly covers the capsule 14 is preferably not lower than -20.degree. C., more preferably not lower than 0.degree. C., and particularly preferably not lower than 10.degree. C. When the material of the cover is a crosslinked rubber composition, the molding temperature T2 is the crosslinking temperature. When the material of the cover is a thermoplastic resin composition, the molding temperature T2 is the maximum temperature reached by the melted resin composition.

[0111] The capsule 14 preferably has a hardness of not less than 30. The capsule 14 having a hardness of not less than 30 can protect the electronic unit 18. From this viewpoint, the hardness is more preferably not less than 40 and particularly preferably not less than 50. The hardness is preferably not greater than 90. In measurement of the hardness of the capsule 14, a Shore D type hardness scale is pressed against the surface of the capsule 14. The temperature at the time of measurement is 23.degree. C.

[0112] Examples of preferable base resins for use in the resin composition of the capsule 14 include polyether ether ketone and polycarbonate. The capsule 14 whose base resin is polyether ether ketone or polycarbonate is less likely to melt during formation of the cover. Furthermore, the capsule 14 has excellent strength. The capsule 14 can protect the electronic unit 18. From the viewpoint of being less likely to melt during formation of the cover, preferable base resins are polycarbonate and polyether ether ketone. The melting point of polycarbonate is 135.degree. C. The melting point of polyether ether ketone is 334.degree. C. From the viewpoint of versatility, a particularly preferable base resin is polycarbonate.

[0113] As described above, the material of the inner cover 6 is a crosslinked rubber composition. As described above, the rubber composition includes a co-crosslinking agent and an organic peroxide. The organic peroxide serves as a crosslinking initiator. A crosslinking initiator having a 1-minute half-life temperature of not higher than 170.degree. C. is preferable. The crosslinking temperature of the rubber composition including this crosslinking initiator is low. When the inner cover 6 is molded from the rubber composition, the capsule 14 is less likely to melt, and the electronic unit 18 is less likely to be damaged. From this viewpoint, the 1-minute half-life temperature of the crosslinking initiator is more preferably not higher than 160.degree. C. and particularly preferably not higher than 155.degree. C. A preferable crosslinking initiator is 1,1-di(t-butylperoxy)cyclohexane. The 1-minute half-life temperature of 1,1-di(t-butylperoxy)cyclohexane is 154.degree. C. A specific example of 1,1-di(t-butylperoxy)cyclohexane is trade name "PERHEXA C" manufactured by NOF Corporation. A crosslinking initiator having a 1-minute half-life temperature of not higher than 170.degree. C. and another crosslinking initiator may be used in combination. The proportion of the crosslinking initiator having a 1-minute half-life temperature of not higher than 170.degree. C. to the entire crosslinking initiator is preferably not less than 30% by weight, more preferably not less than 40% by weight, and particularly preferably not less than 50% by weight.

[0114] As described above, the resin composition of each filling 20 contains a specific gravity adjusting agent. A density Dd of the specific gravity adjusting agent is higher than a density Dr of a matrix (that is, base resin). Therefore, the density of the filling 20 including the specific gravity adjusting agent is high. As is obvious from FIG. 2, the shape of the electronic unit 18 is not a sphere. The electronic unit 18 may cause non-uniformity of the weight distribution in the circumferential direction of the golf ball 2. When the space between the capsule 14 and the electronic unit 18 is filled with the fillings 20 having a high density, non-uniformity of the weight distribution is suppressed. From this viewpoint, the density Dd (true density) of the specific gravity adjusting agent is preferably not lower than 10.0 g/cm.sup.3, more preferably not lower than 15.0 g/cm.sup.3, and particularly preferably not lower than 18.0 g/cm.sup.3. The density is preferably not higher than 30 g/cm.sup.3. A preferable specific gravity adjusting agent is tungsten powder.

[0115] The ratio (Dd/Dr) of the true density Dd of the specific gravity adjusting agent to the density Dr of the base resin of the filling 20 is preferably not less than 5.0, more preferably not less than 10.0, and particularly preferably not less than 15.0.

[0116] The ratio (Vf/Vv) of a total volume Vf of the fillings 20 to a total volume Vv of the vacant spaces 28 is not less than 0/100 and not greater than 100/0. The golf ball 2 in which the ratio (Vf/Vv) is 0/100 has no filling 20. The golf ball 2 in which the ratio (Vf/Vv) is 100/0 has no vacant space 28. The ratio (Vf/Vv) is preferably not less than 30/70, more preferably not less than 50/50, and particularly preferably not less than 70/30.

[0117] The ratio of the sum (Vf+Vv) of the volume Vf and the volume Vv to the volume Vc of the core 4 is preferably not less than 15% and not greater than 55%.

[0118] The golf ball 2 may have a weight for the purpose of adjusting the weight distribution. The weight may be disposed in the capsule 14, or may be disposed between the capsule 14 and the cover. The weight may be included in the cover.

[0119] In the production of the golf ball 2, first, two half shells for the capsule 14 are prepared. Each half shell is generally hemispherical. The electronic unit 18 is fitted into the chamber 26 of the first half shell. The second half shell is combined and fixed to the first half shell. The fixation can be achieved by inserting the pin 22 into the hole 24. The fixation may be achieved by screwing a male screw formed in the first half shell (or the second half shell) and a female screw formed in the second half shell (or the first half shell). The fixation may be achieved by fitting the second half shell to the first half shell. The fixation may be achieved by an adhesive. The spherical capsule 14 is obtained by the fixation.

[0120] The resin composition is injected into the capsule 14. By curing the resin composition, the fillings 20 are formed, and the core 4 is obtained. Before the second half shell is fitted to the first half shell, each half shell may be filled with the resin composition.

[0121] Next, two half shells for the inner cover 6 are prepared. The material of the half shells is an uncrosslinked (or semi-crosslinked) rubber composition. The core 4 is covered with the two half shells. These half shells and the core 4 are placed into a mold, and compressed and heated. Due to the compression and heating, the rubber composition flows. The rubber undergoes a crosslinking reaction due to the heating, and the inner cover 6 is formed. The inner cover 6 may be obtained by injection molding.

[0122] Next, two half shells for the outer cover 8 are prepared. The material of the half shells is a thermoplastic resin composition. The sphere having the core 4 and the inner cover 6 is covered with the two half shells. These half shells and the sphere are placed into a final mold that includes upper and lower mold halves each having a hemispherical cavity and having a large number of pimples on its cavity face, and the outer cover 8 is formed by compression molding. The dimples 10 having a shape that is the inverted shape of the pimples are formed on the outer cover 8. The outer cover 8 may be obtained by injection molding.

[0123] The outer cover 8 is painted as necessary, and the golf ball 2 is obtained.

Second Embodiment

[0124] A golf ball 102 shown in FIG. 3 has a northern hemisphere 104, a southern hemisphere 106, and an equator 108. The equator 108 is a circle. The golf ball 102 can be divided into the northern hemisphere 104 and the southern hemisphere 106 by the plane including this circle. As shown in FIG. 3, the northern hemisphere 104 has a north pole NP, and the southern hemisphere 106 has a south pole SP.

[0125] FIG. 4 is a plan view of the golf ball 102 in FIG. 3. The golf ball 102 has a plurality of dimples 110 on the surface thereof. Of the surface of the golf ball 102, a part other than the dimples 110 is a land 112. In FIG. 3, the dimples 110 are not shown.

[0126] FIG. 5 is a schematic cross-sectional view of the golf ball 102 in FIG. 3. The golf ball 102 includes a core 114, an inner cover 116 positioned outside the core 114, a mid cover 118 positioned outside the inner cover 116, and an outer cover 120 positioned outside the mid cover 118. The golf ball 102 includes a paint layer and a mark layer on the external side of the outer cover 120, but these layers are not shown in the drawing. The paint layer is preferably transparent or translucent. The paint layer may include a large number of particles dispersed in a base material. The golf ball 102 having these particles can have a matte appearance. The outer cover 120 can be viewed through the paint layer.

[0127] As described above, the golf ball 102 has three covers. The number of covers may be 1, 2, or 4 or more. The golf ball 102 may have a layered structure that does not include the inner cover 116. The golf ball 102 may have a layered structure that does not include the mid cover 118. The golf ball 102 may have a layered structure that does not include the outer cover 120. The golf ball 102 may have another cover between the core 114 and the inner cover 116. The golf ball 102 may have another cover between the inner cover 116 and the mid cover 118. The golf ball 102 may have another cover between the mid cover 118 and the outer cover 120. The golf ball 102 may have another cover on the external side of the outer cover 120.

[0128] The golf ball 102 preferably has a diameter of not less than 40 mm and not greater than 45 mm. From the viewpoint of conformity to the rules established by the United States Golf Association (USDA), the diameter is particularly preferably not less than 42.67 mm. In light of suppression of air resistance, the diameter is more preferably not greater than 44 mm and particularly preferably not greater than 42.80 mm.

[0129] The golf ball 102 preferably has a weight of not less than 40 g and not greater than 50 g. In light of attainment of great inertia, the weight is more preferably not less than 44 g and particularly preferably not less than 45.00 g. From the viewpoint of conformity to the rules established by the USGA, the weight is particularly preferably not greater than 45.93 g.

[0130] The core 114 is spherical. The core 114 has a capsule 122, a plurality of separators 124, an electronic unit 126, and a plurality of fillings 128.

[0131] The capsule 122 is spherical. The capsule 122 is hollow. Therefore, the capsule 122 has an internal space. A typical material for the capsule 122 is a resin composition. In the present embodiment, the capsule 122 is transparent.

[0132] FIG. 5 shows four separators 124. Each separator 124 generally has an "L" shape. The separator 124 has a pin 130 or a hole 132. The separator 124 is integrally formed with the capsule 122. Therefore, the material of the separator 124 is the same as that of the capsule 122. A separator 124 formed separately from the capsule 122 may be joined to the capsule 122. The material of the separator 124 may be different from that of the capsule 122. The separator 124 partitions the inside of the capsule 122. These separators 124 form a chamber 134 inside the capsule 122.

[0133] The electronic unit 126 is housed in the capsule 122. Specifically, the electronic unit 126 is housed in the chamber 134. Each separator 124 is in contact with the electronic unit 126. This contact prevents the electronic unit 126 from moving. In other words, the separator 124 fixes the position of the electronic unit 126 with respect to the capsule 122. The separator 124 is a positioning mechanism. The core 114 may have a positioning mechanism other than the separators 124. Positioning mechanisms having various shapes can be adopted. Positioning mechanisms made of various materials can be adopted.

[0134] The electronic unit 126 can detect the behavior of the golf ball 102. Specifically, the electronic unit 126 can detect a speed, a flight angle, a spin rate, a spin rotation axis direction, or a shock of the golf ball 102. As shown in FIG. 5, the electronic unit 126 has a sensor 136. Although not shown, the electronic unit 126 has a control device and a communication device. The electronic unit 126 typically has an acceleration sensor 136. The acceleration sensor 136 is disposed so as to be displaced from a center O of the circle that is the equator 108. The acceleration sensor 136 performs detection on the basis of centrifugal force applied to the golf ball 102. The control device includes a CPU, a RAM, a ROM, and a battery. The control device receives a signal from the sensor 136 and stores the signal in the RAM or the ROM. The CPU adds an operation to the signal from the sensor 136 as necessary. The communication device transmits the signal obtained from the control device, to a device outside the golf ball 102.

[0135] The electronic unit 126 may have a light emitting device. The light emitting device can be turned on by a shock at the time of hitting. The light emitting device may be turned on by remote operation. The electronic unit 126 may have a speaker. The speaker can emit a sound by a shock at the time of hitting. The speaker may emit a sound by remote operation.

[0136] Each filling 128 is positioned between the capsule 122 and the electronic unit 126. The filling 128 is in contact with the inner peripheral surface of the capsule 122 and the electronic unit 126. The filling 128 can suppress a positional displacement of the electronic unit 126. The filling 128 can also absorb a shock transmitted to the electronic unit 126.

[0137] A typical material for the filling 128 is a resin composition. A typical base resin for the resin composition is an epoxy resin. The resin composition can contain a specific gravity adjusting agent. The density of the specific gravity adjusting agent is high. Therefore, the density of the filling 128 is also high. When the space between the capsule 122 and the electronic unit 126 is filled with the fillings 128, non-uniformity of the weight distribution can be suppressed. The density (true density) of the specific gravity adjusting agent is preferably not lower than 10.0 g/cm.sup.3. A preferable specific gravity adjusting agent is tungsten powder.

[0138] Inside the capsule 122, there are vacant spaces 138. The electronic unit 126, the separators 124, the fillings 128, etc., do not exist in the vacant spaces 138. The golf ball 102 may include a core 114 having no vacant space 138. In the core 114 having no vacant space 138, all the portions of the inside of the capsule 122 other than the electronic unit 126 and the separators 124 are filled with the fillings 128.

[0139] As shown in FIG. 5, the inner cover 116 is positioned outside the core 114. The inner cover 116 surrounds the core 114. The inner cover 116 is formed by crosslinking a rubber composition. A rubber composition that is the same as the rubber composition of the inner cover 6 shown in FIG. 2 is suitable for the inner cover 116.

[0140] The inner cover 116 preferably has a thickness of not less than 1.0 mm and not greater than 10.0 mm. The inner cover 116 having a thickness of not less than 1.0 mm can contribute to the resilience performance of the golf ball 102. From this viewpoint, the thickness is more preferably not less than 2.5 mm and particularly preferably not less than 3.5 mm. For the golf ball 102 in which the thickness is not greater than 10.0 mm, a sufficiently large capsule 122 can be adopted. From this viewpoint, the thickness is more preferably not greater than 8.0 mm and particularly preferably not greater than 7.5 mm.

[0141] The inner cover 116 preferably has a hardness of not less than 20 and not greater than 70. The golf ball 102 in which the hardness is not less than 20 has excellent resilience performance. From this viewpoint, the hardness is more preferably not less than 30 and particularly preferably not less than 35. The golf ball 102 in which the hardness is not greater than 70 has excellent feel at impact. From this viewpoint, the hardness is more preferably not greater than 60 and particularly preferably not greater than 50.

[0142] In measurement of the hardness of the inner cover 116, a Shore D type hardness scale is pressed against the surface of the inner cover 116. The temperature at the time of measurement is 23.degree. C.

[0143] The material of the inner cover 116 may be a resin composition. Examples of preferable base polymers for use in the resin composition include ionomer resins, polyurethanes, styrene block-containing thermoplastic elastomers, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, and thermoplastic polyolefin elastomers. A resin described later as the base material of the mid cover 118 or the outer cover 120 can be used for the inner cover 116.

[0144] As shown in FIG. 5, the mid cover 118 is positioned outside the inner cover 116. The mid cover 118 surrounds the inner cover 116. The mid cover 118 is formed from a resin composition. Examples of preferable base polymers for use in the resin composition include ionomer resins, polyurethanes, styrene block-containing thermoplastic elastomers, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, and thermoplastic polyolefin elastomers. Ionomer resins are particularly preferable. Ionomer resins are highly elastic. The golf ball 102 that includes the mid cover 118 including an ionomer resin has excellent resilience performance. The golf ball 102 has excellent flight performance.

[0145] An ionomer resin and another resin may be used in combination. In this case, in light of resilience performance, the ionomer resin is included as the principal component of the base polymer. The proportion of the ionomer resin to the entire base polymer is preferably not less than 50% by weight.

[0146] Examples of preferable ionomer resins include binary copolymers formed with an .alpha.-olefin and an .alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon atoms. A preferable binary copolymer includes 80% by weight or more but 90% by weight or less of an .alpha.-olefin, and 10% by weight or more but 20% by weight or less of an .alpha.,.beta.-unsaturated carboxylic acid. The binary copolymer has excellent resilience performance. Examples of other preferable ionomer resins include ternary copolymers formed with: an .alpha.-olefin; an .alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon atoms; and an .alpha.,.beta.-unsaturated carboxylate ester having 2 to 22 carbon atoms. A preferable ternary copolymer includes 70% by weight or more but 85% by weight or less of an .alpha.-olefin, 5% by weight or more but 30% by weight or less of an .alpha.,.beta.-unsaturated carboxylic acid, and 1% by weight or more but 25% by weight or less of an .alpha.,.beta.-unsaturated carboxylate ester. The ternary copolymer has excellent resilience performance. For the binary copolymer and the ternary copolymer, preferable .alpha.-olefins are ethylene and propylene, while preferable .alpha.,.beta.-unsaturated carboxylic acids are acrylic acid and methacrylic acid. A particularly preferable ionomer resin is a copolymer formed with ethylene and acrylic acid. Another particularly preferable ionomer resin is a copolymer formed with ethylene and methacrylic acid.

[0147] In the binary copolymer and the ternary copolymer, some of the carboxyl groups are neutralized with metal ions. Examples of metal ions for use in neutralization include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions. The neutralization may be carried out with two or more types of metal ions. Particularly suitable metal ions in light of resilience performance and durability of the golf ball 102 are sodium ions, zinc ions, lithium ions, and magnesium ions.

[0148] Specific examples of ionomer resins include trade names "Himilan 1555", "Himilan 1557", "Himilan 1605", "Himilan 1706", "Himilan 1707", "Himilan 1856", "Himilan 1855", "Himilan AM7311", "Himilan AM7315", "Himilan AM7317", "Himilan AM7329", and "Himilan AM7337", manufactured by DOW-MITSUI POLYCHEMICALS CO., LTD.; trade names "Surlyn 6120", "Surlyn 6910", "Surlyn 7930", "Surlyn 7940", "Surlyn 8140", "Surlyn 8150", "Surlyn 8940", "Surlyn 8945", "Surlyn 9120", "Surlyn 9150", "Surlyn 9910", "Surlyn 9945", "Surlyn AD8546", "HPF1000", and "HPF2000", manufactured by E.I. du Pont de Nemours and Company; and trade names "IOTEK 7010", "IOTEK 7030", "IOTEK 7510", "IOTEK 7520", "IOTEK 8000", and "IOTEK 8030", manufactured by ExxonMobil Chemical Corporation. Two or more ionomer resins may be used in combination.

[0149] The resin composition of the mid cover 118 may include a styrene block-containing thermoplastic elastomer together with an ionomer resin. The styrene block-containing thermoplastic elastomer includes a polystyrene block as a hard segment, and a soft segment. A typical soft segment is a diene block. Examples of compounds for the diene block include butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Butadiene and isoprene are preferable. Two or more compounds may be used in combination.

[0150] Examples of styrene block-containing thermoplastic elastomers include styrene-butadiene-styrene block copolymers (SBS), styrene-isoprene-styrene block copolymers (SIS), styrene-isoprene-butadiene-styrene block copolymers (SIBS), hydrogenated SBS, hydrogenated SIS, and hydrogenated SIBS. Examples of hydrogenated SBS include styrene-ethylene-butylene-styrene block copolymers (SEBS). Examples of hydrogenated SIS include styrene-ethylene-propylene-styrene block copolymers (SEPS). Examples of hydrogenated SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymers (SEEPS).

[0151] The resin composition of the mid cover 118 may include a pigment, a dye, a specific gravity adjusting agent, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, and the like in an adequate amount.

[0152] The mid cover 118 preferably has a thickness of not less than 0.3 mm and not greater than 2.5 mm. In the golf ball 102 in which the thickness is not less than 0.3 mm, the mid cover 118 can contribute to the resilience performance of the golf ball 102. From this viewpoint, the thickness is more preferably not less than 0.5 mm and particularly preferably not less than 0.7 mm. In the golf ball 102 in which the thickness is not greater than 2.5 mm, the mid cover 118 does not impair the feel at impact of the golf ball 102. From this viewpoint, the thickness is more preferably not greater than 2.0 mm and particularly preferably not greater than 1.5 mm. The thickness is measured at a position immediately below the land 112.

[0153] The mid cover 118 preferably has a hardness of not less than 40 and not greater than 85. The golf ball 102 in which the hardness is not less than 40 has excellent resilience performance. From this viewpoint, the hardness is more preferably not less than 50 and particularly preferably not less than 55. The golf ball 102 in which the hardness is not greater than 85 has excellent feel at impact. From this viewpoint, the hardness is more preferably not greater than 80 and particularly preferably not greater than 75.

[0154] In measurement of the hardness of the mid cover 118, a Shore D type hardness scale is pressed against the surface of the mid cover 118. The temperature at the time of measurement is 23.degree. C.

[0155] The material of the mid cover 118 may be a crosslinked rubber composition.

[0156] As shown in FIG. 5, the outer cover 120 is positioned outside the mid cover 118. The outer cover 120 surrounds the mid cover 118. The outer cover 120 is formed from a resin composition. A resin composition that is the same as the resin composition of the outer cover 8 shown in FIG. 2 is suitable for the outer cover 120.

[0157] The outer cover 120 preferably has a thickness of not less than 0.3 mm and not greater than 2.0 mm. In the golf ball 102 in which the thickness is not less than 0.3 mm, the outer cover 120 can contribute to spin performance. From this viewpoint, the thickness is more preferably not less than 0.4 mm and particularly preferably not less than 0.5 mm. In the golf ball 102 in which the thickness is not greater than 2.0 mm, the outer cover 120 does not impair resilience performance. From this viewpoint, the thickness is more preferably not greater than 1.5 mm and particularly preferably not greater than 1.0 mm. The thickness is measured at a position immediately below the land 112.

[0158] The outer cover 120 preferably has a hardness of not less than 20 and not greater than 50. The golf ball 102 in which the hardness is not less than 20 has excellent resilience performance. From this viewpoint, the hardness is more preferably not less than 23 and particularly preferably not less than 26. The golf ball 102 in which the hardness is not greater than 50 has excellent feel at impact. From this viewpoint, the hardness is more preferably not greater than 45 and particularly preferably not greater than 40.

[0159] In measurement of the hardness of the outer cover 120, a Shore D type hardness scale is pressed against the surface of the outer cover 120. The temperature at the time of measurement is 23.degree. C.

[0160] The material of the outer cover 120 may be a crosslinked rubber composition.

[0161] The golf ball 102 may have a reinforcing layer between the mid cover 118 and the outer cover 120. The reinforcing layer firmly adheres to the mid cover 118 and also to the outer cover 120. The reinforcing layer suppresses separation of the outer cover 120 from the mid cover 118. The reinforcing layer is formed from a resin composition. Examples of a preferable base polymer of the reinforcing layer include two-component curing type epoxy resins and two-component curing type urethane resins. The reinforcing layer preferably has a thickness of not less than 5 .mu.m and not greater than 30 .mu.m.

[0162] As shown in FIG. 5, the outer cover 120 has a first hemisphere shell 140 and a second hemisphere shell 142. In the present embodiment, the material of the first hemisphere shell 140 is a first resin composition, and the material of the second hemisphere shell 142 is a second resin composition. The color of the second resin composition is different from the color of the first resin composition. Therefore, the color of the second hemisphere shell 142 is different from the color of the first hemisphere shell 140. This color difference is achieved by a difference in the type or amount of a coloring agent. Examples of the coloring agent in the present invention include various additives that affect the color of the golf ball 102. Examples of the coloring agent in the present invention include a pigment, a dye, a brightener, and a fluorescent material. In a preferable embodiment, the base material of the second resin composition is the same as the base material of the first resin composition. In a preferable embodiment, the specifications of the second resin composition except for the type and the amount of the coloring agent are the same as those of the first resin composition.

[0163] In FIG. 5, reference character 144 indicates a virtual line that represents a circle (hereinafter, referred to as a "boundary circle") forming the boundary between the first hemisphere shell 140 and the second hemisphere shell 142. In the present embodiment, the first hemisphere shell 140 belongs to the northern hemisphere 104, and the second hemisphere shell 142 belongs to the southern hemisphere 106. Therefore, the boundary circle 144 coincides with the circle that is the equator 108. Reference character O represents the center of the boundary circle 144. The center O is also the center of the circle that is the equator 108. The center O is also the center of a phantom sphere of the golf ball 102. The phantom sphere is a sphere when it is postulated that no dimples 110 exist on the surface.

[0164] The color of the first hemisphere shell 140 affects the appearance of the northern hemisphere 104. The color of the second hemisphere shell 142 affects the appearance of the southern hemisphere 106. As is obvious from FIG. 3, when the appearance of the golf ball 102 is viewed by a person, the color derived from the first hemisphere shell 140 and the color derived from the second hemisphere shell 142 can be distinguished from each other.

[0165] The mid cover 118 may have a first hemisphere shell and a second hemisphere shell. In this case, the outer cover 120 is preferably transparent. The first hemisphere shell and the second hemisphere shell can be viewed through the outer cover 120. Therefore, the color derived from the first hemisphere shell and the color derived from the second hemisphere shell can be visually distinguished from each other.

[0166] The inner cover 116 may have a first hemisphere shell and a second hemisphere shell. In this case, the mid cover 118 and the outer cover 120 are preferably transparent. The first hemisphere shell and the second hemisphere shell can be viewed through the outer cover 120 and the mid cover 118. Therefore, the color derived from the first hemisphere shell and the color derived from the second hemisphere shell can be visually distinguished from each other.

[0167] Various colors can be adopted for the first hemisphere shell 140 and the second hemisphere shell 142. Examples of a combination of colors (first hemisphere shell, second hemisphere shell) include (white, yellow), (white, orange), (white, pink), (white, red), (white, blue), (yellow, orange), (yellow, pink), (yellow, red), (yellow, blue), (orange, pink), (orange, red), (orange, blue), (pink, red), (pink, blue), and (red, blue). Other color combinations may be adopted.

[0168] In FIG. 5, reference character G represents the center of gravity of the sensor 136. Reference character .theta. represents an angle (absolute value) of a straight line connecting the center O and the center of gravity G with respect to the boundary circle 144. In the present embodiment, the direction of the straight line connecting the center O and the center of gravity G coincides with the direction of a straight line connecting the north pole NP and the south pole SP. Therefore, the angle .theta. is 90.degree..

[0169] When the golf ball 102 is hit with a golf club, the electronic unit 126 detects the behavior of the golf ball 102. The electronic unit 126 transmits a signal regarding the behavior to an external device. Trajectory analysis of the golf ball 102, evaluation of the skill of the golf player, and evaluation of the golf club can be performed on the basis of the signal.

[0170] FIG. 6A is a plan view of the golf ball 102 in FIG. 3 with a golf club head 146, and FIG. 6B is a front view thereof. In FIG. 6B, the golf ball 102 is placed on ground G. The straight line connecting the north pole NP and the south pole SP is parallel to the ground G. Therefore, the circle including the equator 108 is perpendicular to the ground G, and the boundary circle 144 (see FIG. 5) is also perpendicular to the ground G. When the golf club is swung, the head 146 moves in a direction indicated by an arrow A. Due to this movement, the golf ball 102 is launched. The golf ball 102 flies with backspin. The rotation axis of the backspin coincides with the straight line connecting the north pole NP and the south pole SP.

[0171] As described above, the direction of the straight line connecting the center O of the boundary circle 144 and the center of gravity G of the sensor 136 coincides with the direction of the straight line connecting the north pole NP and the south pole SP. Therefore, the direction of the rotation axis of the backspin coincides with the direction of the straight line connecting the center O of the boundary circle 144 and the center of gravity G of the sensor 136. When the golf ball 102 is hit in a posture in which the rotation axis of backspin is to be this direction, accurate measurement can be achieved by the sensor 136.

[0172] As described above, in the golf ball 102, the color derived from the first hemisphere shell 140 and the color derived from the second hemisphere shell 142 can be visually distinguished from each other. Therefore, a measurer can rely on these colors to set the posture of the golf ball 102 prior to hitting. The measurer can easily set a posture in which the direction of the rotation axis of backspin will be appropriate.

[0173] From the viewpoint of ease of setting, the angle .theta. of the straight line connecting the center O and the center of gravity G with respect to the boundary circle 144 is preferably not less than 70.degree. and not greater than 90.degree.. The angle .theta. is more preferably not less than 75.degree. and particularly preferably not less than 80.degree.. The angle .theta. is ideally 90.degree..

[0174] A ratio P1 of a volume Vr of the capsule 122 to a volume Vc of the core 114 is preferably not less than 25% and not greater than 75%. The capsule 122 having a ratio P1 of not less than 25% has excellent durability. The golf ball 102 having the capsule 122 is less likely to break, even when being repeatedly hit. From this viewpoint, the ratio P1 is more preferably not less than 30% and particularly preferably not less than 35%. The golf ball 102 having the capsule 122 having a ratio P1 of not greater than 75% has excellent feel at impact. Therefore, a golf player can hit the golf ball 102 without hesitation. Due to this hit, the behavior of the golf ball 102 can be measured accurately. From this viewpoint, the ratio P1 is more preferably not greater than 73% and particularly preferably not greater than 70%.

[0175] The volume Vr of the capsule 122 is the volume of the material (resin composition) of the capsule 122. In the present embodiment, the capsule 122 is spherical. Therefore, the volume Vr of the capsule 122 can be calculated by the following mathematical formulae.

Vr=4*.pi.*(R1.sup.3-R2.sup.3)/3

R1=D1/2

R2=D2/2

[0176] In these mathematical formulae, D1 represents the outer diameter of the capsule 122, and D2 represents the inner diameter of the capsule 122. In the present embodiment, the outer diameter of the core 114 is equal to the outer diameter D1 of the capsule 122. Therefore, the volume Vc of the core 114 can be calculated by the following mathematical formula.

Vc=4*.pi.*R1.sup.3/3

[0177] The outer diameter D1 of the capsule 122 is preferably not less than 25 mm and not greater than 35 mm. In the capsule 122 having an outer diameter D1 of not less than 25 mm, a sufficiently large electronic unit 126 can be housed. In the electronic unit 126, the sensor 136 can be disposed at a position sufficiently away from the center of the golf ball 102. The capsule 122 can contribute to the accuracy of measurement. From this viewpoint, the outer diameter D1 is more preferably not less than 27 mm and particularly preferably not less than 28 mm. The golf ball 102 in which the outer diameter D1 is not greater than 35 mm is less likely to break, even when being repeatedly hit. Furthermore, the golf ball 102 can have performance close to that of a golf ball 102 including no electronic unit 126. From these viewpoints, the outer diameter D1 is more preferably not greater than 33 mm and particularly preferably not greater than 32 mm.

[0178] As described above, the material of the capsule 122 is a resin composition. The melting point of the capsule 122 (that is, the melting point of the resin composition) is preferably not lower than 100.degree. C. The capsule 122 having a melting point of not lower than 100.degree. C. is less likely to melt during formation of the cover. The capsule 122 can protect the electronic unit 126. From this viewpoint, the melting point is more preferably not lower than 110.degree. C. and particularly preferably not lower than 120.degree. C. The melting point is preferably not higher than 400.degree. C. The melting point of the base resin of the capsule 122 is preferably not lower than 100.degree. C., more preferably not lower than 110.degree. C., and particularly preferably not lower than 120.degree. C. The melting point of the base resin is preferably not higher than 400.degree. C.

[0179] In the present embodiment, the inner cover 116 directly covers the capsule 122. From the viewpoint of suppressing the melting of the capsule 122, the difference (T1-T2) between a melting point T1 of the capsule 122 and a molding temperature T2 of the cover that directly covers the capsule 122 is preferably not lower than -20.degree. C., more preferably not lower than 0.degree. C., and particularly preferably not lower than 10.degree. C. When the material of the cover is a crosslinked rubber composition, the molding temperature T2 is the crosslinking temperature. When the material of the cover is a thermoplastic resin composition, the molding temperature T2 is the maximum temperature reached by the melted resin composition.

[0180] The capsule 122 preferably has a hardness of not less than 30. The capsule 122 having a hardness of not less than 30 can protect the electronic unit 126. From this viewpoint, the hardness is more preferably not less than 40 and particularly preferably not less than 50. The hardness is preferably not greater than 90. In measurement of the hardness of the capsule 122, a Shore D type hardness scale is pressed against the surface of the capsule 122. The temperature at the time of measurement is 23.degree. C.

[0181] Examples of preferable base resins for use in the resin composition of the capsule 122 include polycarbonate and polyether ether ketone. The capsule 122 whose base resin is polycarbonate or polyether ether ketone is less likely to melt during formation of the cover. Furthermore, the capsule 122 has excellent strength. The capsule 122 can protect the electronic unit 126. The melting point of polycarbonate is 135.degree. C. The melting point of polyether ether ketone is 334.degree. C. From the viewpoint of versatility, a particularly preferable base resin is polycarbonate.

[0182] As described above, the material of the inner cover 116 is a crosslinked rubber composition. As described above, the rubber composition includes a co-crosslinking agent and an organic peroxide. The organic peroxide serves as a crosslinking initiator. A crosslinking initiator having a 1-minute half-life temperature of not higher than 170.degree. C. is preferable. The crosslinking temperature of the rubber composition including this crosslinking initiator is low. When the inner cover 116 is molded from the rubber composition, the capsule 122 is less likely to melt, and the electronic unit 126 is less likely to be damaged. From this viewpoint, the 1-minute half-life temperature of the crosslinking initiator is more preferably not higher than 160.degree. C. and particularly preferably not higher than 155.degree. C. A preferable crosslinking initiator is 1,1-di(t-butylperoxy)cyclohexane. The 1-minute half-life temperature of 1,1-di(t-butylperoxy)cyclohexane is 154.degree. C. A specific example of 1,1-di(t-butylperoxy)cyclohexane is trade name "PERHEXA C" manufactured by NOF Corporation. A crosslinking initiator having a 1-minute half-life temperature of not higher than 170.degree. C. and another crosslinking initiator may be used in combination. The proportion of the crosslinking initiator having a 1-minute half-life temperature of not higher than 170.degree. C. to the entire crosslinking initiator is preferably not less than 30% by weight, more preferably not less than 40% by weight, and particularly preferably not less than 50% by weight.

[0183] The ratio (Vf/Vv) of a total volume Vf of the fillings 128 to a total volume Vv of the vacant spaces 138 is not less than 0/100 and not greater than 100/0. The golf ball 102 in which the ratio (Vf/Vv) is 0/100 has no filling 128. The golf ball 102 in which the ratio (Vf/Vv) is 100/0 has no vacant space 138. The ratio (Vf/Vv) is preferably not less than 30/70, more preferably not less than 50/50, and particularly preferably not less than 70/30.

[0184] The ratio of the sum (Vf+Vv) of the volume Vf and the volume Vv to the volume Vc of the core 114 is preferably not less than 15% and not greater than 55%.

[0185] In the production of the golf ball 102, first, two half shells for the capsule 122 are prepared. Each half shell is generally hemispherical. The electronic unit 126 is fitted into the chamber 134 of the first half shell. The second half shell is combined and fixed to the first half shell. The fixation can be achieved by inserting the pin 130 into the hole 132. The fixation may be achieved by screwing a male screw formed in the first half shell (or the second half shell) and a female screw formed in the second half shell (or the first half shell). The fixation may be achieved by fitting the second half shell to the first half shell. The fixation may be achieved by an adhesive. The spherical capsule 122 is obtained by the fixation.

[0186] The resin composition is injected into the capsule 122. By curing the resin composition, the fillings 128 are formed, and the core 114 is obtained. Before the second half shell is fitted to the first half shell, each half shell may be filled with the resin composition.

[0187] Next, two half shells for the inner cover 116 are prepared. The material of the half shells is an uncrosslinked (or semi-crosslinked) rubber composition. The core 114 is covered with the two half shells. These half shells and the core 114 are placed into a mold, and compressed and heated. Due to the compression and heating, the rubber composition flows. The rubber undergoes a crosslinking reaction due to the heating, and the inner cover 116 is formed. The inner cover 116 may be obtained by injection molding.

[0188] Next, the sphere having the core 114 and the inner cover 116 is placed into a mold. A melted resin composition is injected into this mold by injection molding. This resin composition becomes solidified, whereby the mid cover 118 is formed. The mid cover 118 may be formed by compression molding.

[0189] Next, a first half shell and a second half shell for the outer cover 120 are prepared. The material of the first half shell is a resin composition. The material of the second half shell is a resin composition having a color different from the color of the resin composition of the first half shell. The sphere having the core 114, the inner cover 116, and the mid cover 118 is covered with the first half shell and the second half shell. These half shells and the sphere are placed into a final mold, and the outer cover 120 is formed by compression molding. The first hemisphere shell 140 is obtained from the first half shell. The second hemisphere shell 142 is obtained from the second half shell. The second hemisphere shell 142 has a color different from the color of the first hemisphere shell 140. The outer cover 120 may be obtained by injection molding.

[0190] The outer cover 120 is painted as necessary, and the golf ball 102 is obtained. The paint is transparent or translucent.

EXAMPLES

Experiment I

Example 1

[0191] A spherical capsule was prepared. The material of the capsule was polycarbonate (PC). The diameter of the capsule was 30.0 mm. The volume ratio (Vr/Vc) of the capsule was 40%. An electronic unit was fitted into the capsule. A resin composition was injected into the capsule such that the capsule was filled with the resin composition. The resin composition contained an epoxy resin as a base material and tungsten powder as a specific gravity adjusting agent. By curing the resin composition, fillings were formed, and a core was obtained. The ratio (Vf/Vv) of the volume Vf of the fillings to the volume Vv of vacant spaces was 100/0.

[0192] A rubber composition C1 was obtained by kneading 100 parts by weight of a polybutadiene (trade name "BR-730", manufactured by JSR Corporation), 2 parts by weight of 1,1-di(t-butylperoxy)cyclohexane (the aforementioned trade name "PERHEXA C"), 5 parts by weight of zinc oxide (trade name "White Seal"), 0.1 parts by weight of an anti-aging agent (trade name "H-BHT", manufactured by Honshu Chemical Industry Co., Ltd.), 30 parts by weight of zinc diacrylate (trade name "ZN-DA90SN", manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.), and 0.5 parts by weight of diphenyl disulfide (manufactured by Sumitomo Seika Chemicals Co., Ltd.). Half shells were formed from the rubber composition C1. The core was covered with two of the half shells. These half shells and the core were placed into a mold and heated at 120.degree. C. for 50 minutes to form an inner cover.

[0193] A resin composition C5 was obtained by kneading 100 parts by weight of a thermoplastic polyurethane (the aforementioned trade name "Elastollan NY82A"), 4 parts by weight of titanium dioxide, and 0.04 parts by weight of ultramarine blue. Half shells were obtained from the resin composition C5. The sphere consisting of the core and the inner cover was covered with two of these half shells. These half shells and the sphere were placed into a final mold that includes upper and lower mold halves each having a hemispherical cavity and having a large number of pimples on its cavity face, and an outer cover was obtained by compression molding.

[0194] A clear paint including a two-component curing type polyurethane as a base material was applied to this outer cover to obtain a golf ball of Example 1 with a diameter of about 42.7 mm and a weight of about 45.8 g.

Examples 2 to 4

[0195] Golf balls of Examples 2 to 4 were obtained in the same manner as Example 1, except the ratio (Vf/Vv) was as shown in Table 3 below.

Example 5

[0196] A golf ball of Example 5 was obtained in the same manner as Example 1, except the content of the specific gravity adjusting agent in the resin composition of the fillings was zero.

Example 6

[0197] A golf ball of Example 6 was obtained in the same manner as Example 1, except a capsule whose material was polyether ether ketone (PEEK) was used.

Comparative Example 1

[0198] A golf ball of Comparative Example 1 was obtained in the same manner as Example 1, except a capsule whose material was polystyrene (PS) was used and the composition of the inner cover was as shown in Table 4 below.

Examples 7 to 9

[0199] Golf balls of Examples 7 to 9 were obtained in the same manner as Example 1, except the composition of the inner cover was as shown in Table 4 below.

Examples 10 to 13 and Comparative Examples 2 and 3

[0200] Golf balls of Examples 10 to 13 and Comparative Examples 2 and 3 were obtained in the same manner as Example 1, except the volume ratio (Vr/Vc) of the capsule and the volume ratio ((Vf+Vv)/Vc) of the fillings and the vacant spaces were as shown in Table 5 below.

[0201] [Communication Status]

[0202] The communication status between the electronic unit and an external device was rated according to the following criteria. [0203] A: Good [0204] B: Slightly poor [0205] C: Communication is impossible

[0206] The results are shown in Tables 3 to 5 below.

[0207] [Voltage Status]

[0208] The voltage of the power supply of the electronic unit was measured and rated according to the following criteria. [0209] A: Good [0210] B: Slightly poor [0211] C: None

[0212] The results are shown in Tables 3 to 5 below.

[0213] [Durability]

[0214] A golf ball was caused to collide against a metal plate at a speed of 43 m/s by a tester (Ball COR Durability Tester) of Automated Design Corporation. This collision was repeated, and the number of times of the collision until the communication of the electronic unit became impossible was counted. The average of the numbers of times of the collision for five golf balls was calculated and rated according to the following criteria. [0215] A: 60 times or more [0216] B: 20 times or more and 59 times or less [0217] C: 19 times or less

[0218] The results are shown in Tables 3 to 5 below.

[0219] [Feeling]

[0220] Ten golf players hit golf balls and were asked about feel at impact. The evaluation was categorized on the basis of the number of golf players who answered that the feel at impact was good. [0221] A: 8 or more [0222] B: 5 or more and 7 or less [0223] C: 4 or less

[0224] The results are shown in Tables 3 to 5 below.

[0225] [Moment of Inertia]

[0226] Moment of inertia along an X-axis, a Y-axis, and a Z-axis was measured with a measuring instrument ("Model No. 005-002, Series No. M99274" of INERTIA DYNAMICS). Assuming that a parting line of the outer cover is the equator of a globe, each axis passes through the following two points. [0227] X axis: first point (latitude: 90 degrees), second point (latitude: -90 degrees) [0228] Y axis: first point (latitude: 0 degrees, longitude: 0 degrees), second point (latitude: 0 degrees, longitude: 180 degrees) [0229] Z axis: first point (latitude: 0 degrees, longitude: 90 degrees), second point (latitude: 0 degrees, longitude: 270 degrees)

[0230] The evaluation was categorized on the basis of the difference between the maximum and minimum values of the three measurements. [0231] A: The difference is less than 0.50 gcm.sup.2 [0232] B: The difference is 0.50 gcm.sup.2 or more and less than 1.00 gcm.sup.2 [0233] C: The difference is 1.00 gcm.sup.2 or more

[0234] The results are shown in Tables 3 to 5 below.

[0235] [Overall Evaluation]

[0236] Overall evaluation of the above five items was made according to the following criteria.

[0237] S1: All the items have A rank

[0238] S2: One item has B rank and there is no item with C rank

[0239] S3: Two or more items have B rank, or one or more items have C rank

[0240] The results are shown in Tables 3 to 5 below.

TABLE-US-00001 TABLE 1 Rubber Composition (% by weight) C1 C2 Polybutadiene 100 100 PERHEXA C 2 1 PERCUMYL D -- 1 Zinc oxide 5 5 Anti-aging agent 0.1 0.1 Zinc diacrylate 30 30 Diphenyl disulfide 0.5 0.5 PERCUMYL D in Table 1 is dicumyl peroxide (NOF Corporation). The 1-minute half-life temperature thereof is 175.degree. C.

TABLE-US-00002 TABLE 2 Resin Composition (% by weight) C3 C4 C5 TEFABLOC T3221C 30 -- -- Himilan 1605 *1 -- 20 -- Himilan 7329 *2 -- 40 -- Himilan 1557 *3 55 -- -- Himilan 1555 *4 45 20 -- Elastollan NY82A -- -- 100 Titanium dioxide -- -- 4 Ultramarine blue -- -- 0.04 The details of the compounds in Table 2 are as follows. *1: sodium ion-neutralized ethylene-methacrylic acid copolymer *2: zinc ion-neutralized ethylene-methacrylic acid copolymer *3: zinc ion-neutralized ethylene-methacrylic acid copolymer *4: sodium ion-neutralized ethylene-acrylic acid copolymer

TABLE-US-00003 TABLE 3 Evaluation Results Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Capsule PC PC PC PC PC D1 (mm) 30.0 30.0 30.0 30.0 30.0 Melting point (.degree. C.) 135 135 135 135 135 Hardness (Shore D) 60 60 60 60 60 Vr/Vc 40% 40% 40% 40% 40% Filling (Vf + Vv)/Vc 35% 35% 35% 35% 35% Vf/Vv 100/0 50/50 30/70 0/100 100/0 Specific gravity Con- Con- Con- Con- N.c. adjusting agent tained tained tained tained Inner cover C1 C1 C1 C1 C1 Diameter (mm) 39.8 39.8 39.8 39.8 39.8 Molding temp. (.degree. C.) 120 120 120 120 120 Molding time (min) 50 50 50 50 50 Hardness (Shore D) 45 45 45 45 45 Outer cover C5 C5 C5 C5 C5 Thickness (mm) 1.45 1.45 1.45 1.45 1.45 Hardness (Shore D) 29 29 29 29 29 Weight (g) 45.8 45.6 45.4 45.2 45.8 Communication A A A A A Voltage A A A A A Durability A A B B A Feeling A A A A A Moment of inertia A A A A B Overall evaluation S1 S1 S2 S2 S2 PC: polycarbonate N.C.: Not contained

TABLE-US-00004 TABLE 4 Evaluation Results Comp. Ex. 6 Ex. 1 Ex. 7 Ex. 8 Ex. 9 Capsule PEEK PS PC PC PC D1 (mm) 30.0 30.0 30.0 30.0 30.0 Melting point (.degree. C.) 334 65-76 135 135 135 Hardness (Shore D) 70 65 60 60 60 Vr/Vc 40% 40% 40% 40% 40% Filling (Vf + Vv)/Vc 35% 35% 35% 35% 35% Vf/Vv 100/0 100/0 100/0 100/0 100/0 Specific gravity Con- Con- Con- Con- Con- adjusting agent tained tained tained tained tained Inner cover C1 C3 C2 C3 C4 Diameter (mm) 39.8 39.8 39.8 39.8 39.8 Molding temp. (.degree. C.) 120 120 150 120 120 Molding time (min) 50 10 25 5 5 Hardness (Shore D) 45 45 45 45 63 Outer cover C5 C5 C5 C5 C5 Thickness (mm) 1.45 1.45 1.45 1.45 1.45 Hardness (Shore D) 29 29 29 29 29 Weight (g) 45.8 45.8 45.8 45.8 45.8 Communication A C A A A Voltage A A B A A Durability A C A A A Feeling A A A A B Moment of inertia A A A A A Overall evaluation S1 S3 S2 S1 S2 PEEK: polyether ether ketone PC: polycarbonate PS: polystyrene

TABLE-US-00005 TABLE 5 Evaluation Results Comp. Ex. 2 Ex. 10 Ex. 11 Capsule PC PC PC D1 (mm) 30.0 30.0 30.0 Melting point (.degree. C.) 135 135 135 Hardness (Shore D) 60 60 60 Vr/Vc 20% 25% 50% Filling (Vf + Vv)/Vc 55% 50% 25% Vf/Vv 100/0 100/0 100/0 Specific gravity Contained Contained Contained adjusting agent Inner cover C1 C1 C1 Diameter (mm) 39.8 39.8 39.8 Molding temp. (.degree. C.) 120 120 120 Molding time (min) 50 50 50 Hardness (Shore D) 45 45 45 Outer cover C5 C5 C5 Thickness (mm) 1.45 1.45 1.45 Hardness (Shore D) 29 29 29 Weight (g) 45.8 45.8 45.8 Communication A A A Voltage A A A Durability C B A Feeling A A A Moment of inertia A A A Overall evaluation S3 S2 S1 Comp. Ex. 12 Ex. 13 Ex. 3 Capsule PC PC PC D1 (mm) 30.0 30.0 32.0 Melting point (.degree. C.) 135 135 135 Hardness (Shore D) 60 60 60 Vr/Vc 60% 70% 80% Filling (Vf + Vv)/Vc 15% 5% 0% Vf/Vv 100/0 100/0 -- Specific gravity Contained Contained Contained adjusting agent Inner cover C1 C1 C1 Diameter (mm) 39.8 39.8 39.8 Molding temp. (.degree. C.) 120 120 120 Molding time (min) 50 50 50 Hardness (Shore D) 45 45 45 Outer cover C5 C5 C5 Thickness (mm) 1.45 1.45 1.45 Hardness (Shore D) 29 29 29 Weight (g) 45.8 45.8 45.8 Communication A A A Voltage A A A Durability A A A Feeling B B C Moment of inertia A A A Overall evaluation S2 S2 S3 PC: polycarbonate

[0241] As shown in Tables 3 to 5, the golf ball of each Example is excellent in various performance characteristics. From the evaluation results, advantages of the present invention are clear.

Experiment II

Example 1

[0242] A spherical capsule was prepared. The material of the capsule was polycarbonate (PC). The diameter of the capsule was 30.0 mm. The volume ratio (Vr/Vc) of the capsule was 40%. An electronic unit was fitted into the capsule such that the angle .theta. was 90.degree.. A resin composition was injected into the capsule such that the capsule was filled with the resin composition. The resin composition contained an epoxy resin as a base material and tungsten powder as a specific gravity adjusting agent. By curing the resin composition, fillings were formed, and a core was obtained. The ratio (Vf/Vv) of the volume Vf of the fillings to the volume Vv of vacant spaces was 100/0.

[0243] A rubber composition C1 was obtained by kneading 100 parts by weight of a polybutadiene (trade name "BR-730", manufactured by JSR Corporation), 2 parts by weight of 1,1-di(t-butylperoxy)cyclohexane (the aforementioned trade name "PERHEXA C"), 5 parts by weight of zinc oxide (trade name "White Seal"), 0.1 parts by weight of an anti-aging agent (trade name "H-BHT", manufactured by Honshu Chemical Industry Co., Ltd.), 30 parts by weight of zinc diacrylate (trade name "ZN-DA90SN", manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.), and 0.5 parts by weight of diphenyl disulfide (manufactured by Sumitomo Seika Chemicals Co., Ltd.). Half shells were formed from the rubber composition C1. The core was covered with two of the half shells. These half shells and the core were placed into a mold and heated at 120.degree. C. for 50 minutes to form an inner cover.

[0244] A resin composition C5 was obtained by kneading 50 parts by weight of an ionomer resin (the aforementioned trade name "Himilan AM7329"), 25 parts by weight of another ionomer resin (the aforementioned trade name "Himilan 1605"), 25 parts by weight of still another ionomer resin (the aforementioned trade name "Surlyn 8150"), an appropriate amount of barium sulfate, and 4 parts by weight of titanium dioxide. The sphere consisting of the core and the inner cover was placed into a mold, and the melted resin composition C5 was injected so as to cover the sphere to obtain a mid cover. The thickness of the mid cover was 1.0 mm.

[0245] A resin composition C6 was obtained by kneading 100 parts by weight of a thermoplastic polyurethane (the aforementioned trade name "Elastollan NY82A"), 4 parts by weight of titanium dioxide, and 0.04 parts by weight of ultramarine blue. A first half shell was obtained from the resin composition C6. The color of the first half shell was white. A resin composition C7 was obtained by kneading 100 parts by weight of a thermoplastic polyurethane (the aforementioned trade name "Elastollan NY82A"), 0.1 parts by weight of titanium dioxide, and 3 parts by weight of a yellow pigment. A second half shell was obtained from the resin composition C7. The color of the second half shell was yellow. The sphere consisting of the core, the inner cover, and the mid cover was covered with the first half shell and the second half shell. These half shells and the sphere were placed into a final mold that includes upper and lower mold halves each having a hemispherical cavity and having a large number of pimples on its cavity face, and an outer cover was obtained by compression molding. A first hemisphere shell was obtained from the first half shell. A second hemisphere shell was obtained from the second half shell. The color of the first hemisphere shell was white. The color of the second hemisphere shell was yellow.

[0246] A clear paint including a two-component curing type polyurethane as a base material was applied to this outer cover to obtain a golf ball of Example 1 with a diameter of about 42.7 mm and a weight of about 45.8 g. A paint film obtained from the clear paint was colorless and transparent.

Examples 2 and 3

[0247] Golf balls of Examples 2 and 3 were obtained in the same manner as Example 1, except the direction of the electronic unit was changed and the angle .theta. was as shown in Table 9 below.

Example 4

[0248] A golf ball of Example 4 was obtained in the same manner as Example 1, except a capsule whose material was polyether ether ketone (PEEK) was used.

Example 5

[0249] A golf ball of Example 5 was obtained in the same manner as Example 1, except a capsule whose material was polystyrene (PS) was used and the composition of the inner cover was as shown in Table 9 below.

Examples 6 to 11

[0250] Golf balls of Examples 6 to 11 were obtained in the same manner as Example 1, except the volume ratio (Vr/Vc) of the capsule and the volume ratio ((Vf+Vv)/Vc) of the fillings and the vacant spaces were as shown in Table 10 below.

Examples 12 to 14

[0251] Golf balls of Examples 12 to 14 were obtained in the same manner as Example 1, except the composition of the inner cover was as shown in Table 11 below.

Comparative Examples 1 and 2

[0252] A golf ball of Comparative Example 1 was obtained in the same manner as Example 1, except an outer cover was formed of two half shells obtained from the resin composition C6. The golf ball was white as a whole. A golf ball of Comparative Example 2 was obtained in the same manner as Example 1, except an outer cover was formed of two half shells obtained from the resin composition C6 and the angle .theta. was 30.degree.. The golf ball was white as a whole.

[0253] [Ease of Setting]

[0254] A golf ball was set such that the plane including the boundary circle was perpendicular to the ground, and the golf ball was hit with a golf club. Ratings were made according to the following criteria. [0255] Good: The setting is easy [0256] Bad: The setting is difficult

[0257] The results are shown in Tables 9 to 11 below.

[0258] [Stability]

[0259] A driver with a head made of a titanium alloy (trade name "XXIO 11", manufactured by Sumitomo Rubber Industries, Ltd., shaft hardness: R, loft angle: 10.5.degree.) was attached to a swing machine manufactured by Golf Laboratories, Inc. A golf ball was hit under a condition of a head speed of 40 m/sec, and the initial speed was measured. The results of 12 measurements were rated according to the following criteria. [0260] A: The variation is small [0261] B: The variation is slightly large [0262] C: The variation is large

[0263] The results are shown in Tables 9 to 11 below.

[0264] [Communication Status]

[0265] The communication status between the electronic unit and an external device was rated according to the following criteria. [0266] A: Good [0267] B: Slightly poor [0268] C: Communication is impossible

[0269] The results are shown in Tables 9 to 11 below.

[0270] [Voltage Status]

[0271] The voltage of the power supply of the electronic unit was measured and rated according to the following criteria. [0272] A: Good [0273] B: Slightly poor [0274] C: None

[0275] The results are shown in Tables 9 to 11 below.

[0276] [Durability]

[0277] A golf ball was caused to collide against a metal plate at a speed of 43 m/s by a tester (Ball COR Durability Tester) of Automated Design Corporation. This collision was repeated, and the number of times of the collision until the communication of the electronic unit became impossible was counted. The average of the numbers of times of the collision for five golf balls was calculated and rated according to the following criteria. [0278] A: 60 times or more [0279] B: 20 times or more and 59 times or less [0280] C: 19 times or less

[0281] The results are shown in Tables 9 to 11 below.

[0282] [Feeling]

[0283] Ten golf players hit golf balls and were asked about feel at impact. The evaluation was categorized on the basis of the number of golf players who answered that the feel at impact was good. [0284] A: 8 or more [0285] B: 5 or more and 7 or less [0286] C: 4 or less

[0287] The results are shown in Tables 9 to 11 below.

[0288] [Overall Evaluation]

[0289] Overall evaluation of the above six items was made according to the following criteria.

[0290] S1: The ease of setting is "Good". [0291] All other evaluation items have A rank.

[0292] S2: The ease of setting is "Good". [0293] Other evaluation items have B rank but no C rank.

[0294] S3: The ease of setting is "Good". [0295] Other evaluation items have C rank.

[0296] S4: The ease of setting is "Bad".

[0297] The results are shown in Tables 9 to 11 below.

TABLE-US-00006 TABLE 6 Composition of Inner Cover (parts by weight) C1 C2 Polybutadiene 100 100 PERHEXA C 2 1 PERCUMYL D -- 1 Zinc oxide 5 5 Anti-aging agent 0.1 0.1 Zinc diacrylate 30 30 Organic sulfur compound 0.5 0.5

[0298] Trade name "PERCUMYL D" in Table 6 is dicumyl peroxide (NOF Corporation). The 1-minute half-life temperature thereof is 175.degree. C.

TABLE-US-00007 TABLE 7 Composition of Inner Cover (parts by weight) C3 C4 TEFABLOC T3221C 30 -- Himilan 1605 -- 20 Himilan 7329 -- 40 Himilan 1557 55 -- Himilan 1555 45 20 Material hardness (Shore D) 45 63

[0299] Trade name "TEFABLOC T3221C" in Table 7 is a styrene block-containing thermoplastic elastomer.

TABLE-US-00008 TABLE 8 Composition of Mid Cover/Outer Cover (parts by weight) C5 C6 C7 Himilan AM7329 50 -- -- Himilan 1605 25 -- -- Surlyn 8150 25 -- -- Elastollan NY82A -- 100 100 Barium sulfate Appropriat -- -- amount Titanium dioxide 4 4 0.1 Ultramarine blue -- 0.04 -- Yellow pigment -- -- 3 Hardness (Shore D) 68 29 29

TABLE-US-00009 TABLE 9 Evaluation Results Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Capsule PC PC PC PEEK PS D1 (mm) 30.0 30.0 30.0 30.0 30.0 Melting point (.degree. C.) 135 135 135 334 65-76 Hardness (Shore D) 60 60 60 70 65 Vr/Vc 40% 40% 40% 40% 40% Filling (Vf + Vv)/Vc 35% 35% 35% 35% 35% Vf/Vv 100/0 100/0 100/0 100/0 100/0 Inner cover C1 C1 C1 C1 C3 Diameter (mm) 39.7 39.7 39.7 39.7 39.7 Molding temp. (.degree. C.) 120 120 120 120 120 Molding time (min) 50 50 50 50 10 Hardness (Shore D) 45 45 45 45 45 Mid cover C5 C5 C5 C5 C5 Thickness (mm) 1.0 1.0 1.0 1.0 1.0 Hardness (Shore D) 68 68 68 68 68 Hemisphere shell C6/C7 C6/C7 C6/C7 C6/C7 C6/C7 First/Second Thickness (mm) 0.5 0.5 0.5 0.5 0.5 Hardness (Shore D) 29 29 29 29 29 .theta. (deg.) 90 70 30 90 90 Setting Good Good Good Good Good Stability A B C A A Communication A A A A C Voltage A A A A A Durability A A A A C Feeling A A A A A Overall evaluation S1 S2 S3 S1 S3

TABLE-US-00010 TABLE 10 Evaluation Results Ex. 6 Ex. 7 Ex. 8 Capsule PC PC PC D1 (mm) 30.0 30.0 30.0 Melting point (.degree. C.) 135 135 135 Hardness (Shore D) 60 60 60 Vr/Vc 20% 25% 50% Filling (Vf + Vv)/Vc 55% 50% 50% Vf/Vv 100/0 100/0 100/0 Inner cover C1 C1 C1 Diameter (mm) 39.7 39.7 39.7 Molding temp. (.degree. C.) 120 120 120 Molding time (min) 50 50 50 Hardness (Shore D) 45 45 45 Mid cover C5 C5 C5 Thickness (mm) 1.0 1.0 1.0 Hardness (Shore D) 68 68 68 Hemisphere shell C6/C7 C6/C7 C6/C7 First/Second Thickness (mm) 0.5 0.5 0.5 Hardness (Shore D) 29 29 29 .theta. (deg.) 90 90 90 Setting Good Good Good Stability A A A Communication A A A Voltage A A A Durability C B A Feeling A A A Overall evaluation S3 S2 S1 Ex. 9 Ex. 10 Ex. 11 Capsule PC PC PC D1 (mm) 30.0 30.0 32.0 Melting point (.degree. C.) 135 135 135 Hardness (Shore D) 60 60 60 Vr/Vc 60% 70% 80% Filling (Vf + Vv)/Vc 50% 5% 0% Vf/Vv 100/0 100/0 -- Inner cover C1 C1 C1 Diameter (mm) 39.7 39.7 39.7 Molding temp. (.degree. C.) 120 120 120 Molding time (min) 50 50 50 Hardness (Shore D) 45 45 45 Mid cover C5 C5 C5 Thickness (mm) 1.0 1.0 1.0 Hardness (Shore D) 68 68 68 Hemisphere shell C6/C7 C6/C7 C6/C7 First/Second Thickness (mm) 0.5 0.5 0.5 Hardness (Shore D) 29 29 29 .theta. (deg.) 90 90 90 Setting Good Good Good Stability A A A Communication A A A Voltage A A A Durability A A A Feeling B B C Overall evaluation S2 S2 S3

TABLE-US-00011 TABLE 11 Evaluation Results Comp. Comp. Ex. 12 Ex. 13 Ex. 14 Ex. 1 Ex. 2 Capsule PC PC PC PC PC D1 (mm) 30.0 30.0 30.0 30.0 30.0 Melting point (.degree. C.) 135 135 135 135 135 Hardness (Shore D) 60 60 60 60 60 Vr/Vc 40% 40% 40% 40% 40% Filling (Vf + Vv)/Vc 35% 35% 35% 35% 35% Vf/Vv 100/0 100/0 100/0 100/0 100/0 Inner cover C2 C3 C4 C1 C1 Diameter (mm) 39.7 39.7 39.7 39.7 39.7 Molding temp. (.degree. C.) 150 120 120 120 120 Molding time (min) 25 5 5 50 50 Hardness (Shore D) 45 45 63 45 45 Mid cover C5 C5 C5 C5 C5 Thickness (mm) 1.0 1.0 1.0 1.0 1.0 Hardness (Shore D) 68 68 68 68 68 Hemisphere shell C6/C7 C6/C7 C6/C7 C6/C6 C6/C6 First/Second Thickness (mm) 0.5 0.5 0.5 0.5 0.5 Hardness (Shore D) 29 29 29 29 29 .theta. (deg.) 90 90 90 90 30 Setting Good Good Good Bad Bad Stability A A A A C Communication A A A A A Voltage B A A A A Durability A A A A A Feeling A A B A A Overall evaluation S2 S1 S2 S4 S4

[0300] As shown in Tables 9 to 11, the golf ball of each Example is excellent in various performance characteristics. From the evaluation results, advantages of the present invention are clear.

[0301] The golf ball according to the present invention is suitable for trajectory analysis, evaluation of the skill of a golf player, and evaluation of a golf club. The above descriptions are merely illustrative examples, and various modifications can be made without departing from the principles of the present invention.

Claims

1. A golf ball comprising a core and one or more covers positioned outside the core, wherein the core has an electronic unit for detecting behavior of the golf ball and a capsule in which the electronic unit is housed and which has a melting point of not lower than 100.degree. C., and a ratio P1 of a volume Vr of the capsule to a volume Vc of the core is not less than 25% and not greater than 75%.

2. The golf ball according to claim 1, wherein the core has, in the capsule, a positioning mechanism capable of fixing a position of the electronic unit with respect to the capsule by attaching the electronic unit.

3. The golf ball according to claim 2, wherein the positioning mechanism is a separator fixed to the capsule and partitioning an inside of the capsule.

4. The golf ball according to claim 1, wherein the core has a filling positioned between the capsule and the electronic unit.

5. The golf ball according to claim 4, wherein a base material of the filling is an epoxy resin.

6. The golf ball according to claim 4, wherein the filling includes a matrix and a specific gravity adjusting agent dispersed in the matrix and having a density higher than a density of the matrix.

7. The golf ball according to claim 6, wherein the specific gravity adjusting agent is tungsten powder.

8. The golf ball according to claim 1, wherein the capsule has a Shore D hardness of not less than 30.

9. The golf ball according to claim 1, wherein a material of the capsule is a resin composition, and a base resin of the resin composition is polycarbonate or polyether ether ketone.

10. The golf ball according to claim 1, wherein the one or more covers include a cover formed by crosslinking a rubber composition, and the rubber composition includes (1) a base rubber, (2) a co-crosslinking agent, and (3) a crosslinking initiator having a 1-minute half-life temperature of not higher than 170.degree. C.

11. The golf ball according to claim 1, wherein the one or more covers include a cover whose material is a resin composition, and a base resin of the resin composition is an ionomer resin or a polyurethane.

12. The golf ball according to claim 1, wherein the one or more covers include an inner cover positioned outside the core and an outer cover positioned outside the inner cover, the inner cover is formed by crosslinking a rubber composition, and a material of the outer cover is a resin composition.

13. The golf ball according to claim 12, wherein the inner cover has a thickness of not less than 1.0 mm, the inner cover has a Shore D hardness of not greater than 50, the outer cover has a thickness of not less than 1.0 mm, and the outer cover has a Shore D hardness of not greater than 50.

14. A golf ball comprising a core and one or more covers positioned outside the core, wherein the core has an electronic unit for detecting behavior of the golf ball, and any one of the one or more covers has a first hemisphere shell and a second hemisphere shell having a color different from a color of the first hemisphere shell.

15. The golf ball according to claim 14, wherein the electronic unit has a sensor, and an angle of a straight line connecting a center of a circle forming a boundary between the first hemisphere shell and the second hemisphere shell and a center of gravity of the sensor, to the circle, is not less than 70.degree. and not greater than 90.degree..

16. The golf ball according to claim 14, wherein the core has a capsule having a melting point of not lower than 100.degree. C., and the electronic unit is housed in the capsule.

17. The golf ball according to claim 16, wherein a ratio P1 of a volume Vr of the capsule to a volume Vc of the core is not less than 25% and not greater than 75%.

18. The golf ball according to claim 16, wherein the core has, in the capsule, a positioning mechanism capable of fixing a position of the electronic unit with respect to the capsule by attaching the electronic unit.

19. The golf ball according to claim 18, wherein the positioning mechanism is a separator fixed to the capsule and partitioning an inside of the capsule.

20. The golf ball according to claim 16, wherein the core has a filling positioned between the capsule and the electronic unit.

21. The golf ball according to claim 16, wherein a material of the capsule is a resin composition, and a base resin of the resin composition is polycarbonate or polyether ether ketone.

22. The golf ball according to claim 14, wherein the one or more covers include an inner cover positioned outside the core and an outer cover positioned outside the inner cover, the inner cover is formed by crosslinking a rubber composition, the outer cover has the first hemisphere shell and the second hemisphere shell, a material of the first hemisphere shell is a resin composition, and a material of the second hemisphere shell is a resin composition different from the resin composition of the first hemisphere shell.

23. The golf ball according to claim 22, wherein the rubber composition includes (1) a base rubber, (2) a co-crosslinking agent, and (3) a crosslinking initiator having a 1-minute half-life temperature of not higher than 170.degree. C.