JP6819265B2 - Golf ball - Google Patents

Description

The present invention relates to a golf ball. In particular, the present invention relates to a golf ball having a core, an intermediate layer, a cover and dimples.

The face of a golf club has a loft angle. When a golf ball is hit by this golf club, the golf ball undergoes backspin due to the loft angle. A golf ball flies with a backspin.

A golf player's greatest concern with a golf ball is distance. Players place particular importance on distance on driver shots. Various proposals have been made for improving flight performance. Japanese Unexamined Patent Publication No. 2010-188199 discloses a golf ball having a core having a large surface hardness and a small center hardness. The speed of backspin when this golf ball is hit by a driver is small.

A golf ball has a large number of dimples on its surface. The dimples disturb the flow of air around the golf ball during flight, causing turbulent separation. This phenomenon is called "turbulence". The turbulence shifts the point of separation of air from the golf ball backwards, reducing drag. The turbulence promotes the deviation between the upper peeling point and the lower peeling point of the golf ball due to backspin, and enhances the lift acting on the golf ball. The reduction of drag and the improvement of lift are referred to as the "dimple effect". Good dimples better disrupt the flow of air. Excellent dimples produce a large flight distance.

Various proposals have been made regarding dimples. Japanese Unexamined Patent Publication No. 4-109968 discloses a golf ball in which a hemispherical dimple pattern can be divided into 6 units. Japanese Unexamined Patent Publication No. 2004-243124 discloses a golf ball in which a dimple pattern near the pole can be divided into 4 units and a dimple pattern near the equator can be divided into 5 units. Japanese Unexamined Patent Publication No. 2011-10667 discloses a golf ball in which a parameter depending on the dimple shape is within a predetermined range.

JP-A-2010-188199 Japanese Unexamined Patent Publication No. 4-1099668 JP-A-2004-243124 Japanese Unexamined Patent Publication No. 2011-10667

Players want a golf ball with excellent flight performance on driver shots. There is room for improvement in flight performance.

In golf, a golf ball is hit by a wood type club, an iron type club, a hybrid type club (utility), a putter, or the like. The shot feeling at the time of hitting is a concern of the player. In general, players want a golf ball with a soft feel.

When hitting with a wood type club, an iron type club or a hybrid type club, the frequency of missed shots is high. Therefore, the player is insensitive to the shot feeling when hitting a golf ball with these clubs.

On the other hand, in putting, the golf ball is often hit at the sweet spot of the putter. Players are sensitive to the shot feeling when putting. The player wants a golf ball that gives a soft shot feeling by putting.

An object of the present invention is to provide a golf ball having excellent flight performance on a driver shot and a shot feeling on putting.

The golf ball according to the present invention includes a core, one or more intermediate layers located outside the core, and a cover located outside the intermediate layers. The central shore C hardness Ho in the core, the surface shore C hardness Hs, the shore C hardness Hm (min) of the layer having the lowest hardness among the intermediate layers, and the shore C hardness Hc of the cover are obtained from the following mathematical formula (i). (Iv) is satisfied.
Hs-Ho> 15 (i)
Hc − Hm (min)> 20 (ii)
-10 <Hm (min) -Ho <15 (iii)
5 <Hc − Hs <20 (iv)
The hardness Hc of the cover is larger than the shore C hardness Hm (max) of the layer having the highest hardness among the intermediate layers. The golf ball further comprises a plurality of dimples on its surface. When the spherical polar coordinates of a point located on the surface of the virtual sphere of this golf ball, where the latitude is θ (degree) and the longitude is φ (degree), are represented by (θ, φ),
(1) The first axis Ax1 passing through the point Pn1 whose coordinates are (75,270) and the point Ps1 whose coordinates are (-75,90),
(2) The second axis Ax2, which passes through the point Pn2 whose coordinates are (60,270) and the point Ps2 whose coordinates are (-60,90).
(3) Third axis Ax3, which passes through the point Pn3 whose coordinates are (45,270) and the point Ps3 whose coordinates are (-45,90).
(4) Fourth axis Ax4, which passes through the point Pn4 whose coordinates are (30,270) and the point Ps4 whose coordinates are (-30,90).
(5) The fifth axis Ax5, which passes through the point Pn5 whose coordinates are (15,270) and the point Ps5 whose coordinates are (-15,90).
(6) The sixth axis Ax6, which passes through the point Pn6 whose coordinates are (75,0) and the point Ps6 whose coordinates are (-75,180).
(7) The seventh axis Ax7, which passes through the point Pn7 whose coordinates are (60,0) and the point Ps7 whose coordinates are (-60,180).
(8) The eighth axis Ax8, which passes through the point Pn8 whose coordinates are (45,0) and the point Ps8 whose coordinates are (-45,180).
(9) Ninth axis Ax9, which passes through the point Pn9 whose coordinates are (30,0) and the point Ps9 whose coordinates are (-30,180).
(10) The tenth axis Ax10, which passes through the point Pn10 whose coordinates are (15.0) and the point Ps10 whose coordinates are (-15,180).
(11) The eleventh axis Ax11, which passes through the point Pn11 whose coordinates are (75,90) and the point Ps11 whose coordinates are (-75,270).
(12) The twelfth axis Ax12, which passes through the point Pn12 whose coordinates are (60,90) and the point Ps12 whose coordinates are (-60,270).
(13) The thirteenth axis Ax13, which passes through the point Pn13 whose coordinates are (45,90) and the point Ps13 whose coordinates are (-45,270).
(14) The fourteenth axis Ax14, which passes through the point Pn14 whose coordinates are (30,90) and the point Ps14 whose coordinates are (-30,270).
And (15) the fifteenth axis Ax15 passing through the point Pn15 whose coordinates are (15,90) and the point P15s whose coordinates are (-15,270).
For each of the 15 axes Ax
(A) A step in which a great circle existing on the surface of the virtual sphere and orthogonal to the axis Ax is assumed.
(B) A step in which two small circles existing on the surface of the virtual sphere, orthogonal to the axis Ax, and having an absolute value of the central angle with the great circle of 30 ° are assumed.
(C) A step in which the surface of the golf ball is partitioned by these small circles and the area of the surface sandwiched between these small circles is identified.
(D) A step in which 30240 points are determined in the above region at a central angle of 3 ° in the axial direction and at a central angle of 0.25 ° in the rotation direction.
(E) A step in which the length L1 of the perpendicular line drawn from each point on the axis Ax is calculated.
(F) A step in which 21 lengths L1 calculated based on 21 perpendicular lines arranged in the axial direction are totaled to calculate a total length L2.
(G) A step in which a Fourier transform is performed on 1440 data groups having a total length of L2 calculated along the rotation direction to obtain a converted data group.
(H) The minimum value of the 15 peak values obtained by executing the step of calculating the peak value and the order of the maximum peak of the conversion data group is 95 mm or more. The minimum value of the order of 15 obtained by executing these steps (a)-(h) is 27 or more. The maximum value of the order of 15 obtained by executing these steps (a)-(h) is 37 or less. The average value of the order of 15 obtained by executing these steps (a)-(h) is 30 or more and 34 or less.

Preferably, the total thickness of the cover and the intermediate layer is 2.8 mm or less.

Preferably, the average of the 15 peak values obtained by performing these steps (a)-(h) is 200 mm or more.

Preferably, the total volume of the dimples is 450 mm ³ or more and 750 mm ³ or less.

The golf ball according to the present invention has excellent resilience performance when hit by a driver. The spin speed when this golf ball is hit by a driver is small. Further, the dimple pattern of this golf ball is excellent in aerodynamic characteristics. This golf ball has excellent flight performance when hit by a driver.

The impact when this golf ball is hit with a putter is small. When this golf ball is hit with a putter, the shot feeling is soft.

This golf ball is excellent in both flight performance when hit by a driver and shot feeling when hit by a putter.

FIG. 1 is a schematic cross-sectional view showing a golf ball according to an embodiment of the present invention. FIG. 2 is an enlarged front view showing the golf ball of FIG. FIG. 3 is a plan view showing the golf ball of FIG. FIG. 4 is an enlarged cross-sectional view showing a part of the golf ball of FIG. FIG. 5 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 6 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 7 is a schematic cross-sectional view for explaining the evaluation method of the golf ball of FIG. FIG. 8 is a schematic cross-sectional view for explaining the evaluation method of the golf ball of FIG. FIG. 9 is a graph showing the evaluation results of the golf ball of FIG. FIG. 10 is a graph showing the evaluation results of the golf ball of FIG. FIG. 11 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 12 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 13 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 14 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 15 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 16 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 17 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 18 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 19 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 20 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 21 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 22 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 23 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 24 is a schematic diagram for explaining the evaluation method of the golf ball of FIG. FIG. 25 is a front view showing a golf ball according to a second embodiment of the present invention. FIG. 26 is a plan view showing the golf ball of FIG. 25. FIG. 27 is a front view showing a golf ball according to a third embodiment of the present invention. FIG. 28 is a plan view showing the golf ball of FIG. 27. FIG. 29 is a front view showing the golf ball according to Comparative Example 1. FIG. 30 is a plan view showing the golf ball of FIG. 29. FIG. 31 is a front view showing a golf ball according to Comparative Example 2. FIG. 32 is a plan view showing the golf ball of FIG. 31. FIG. 33 is a front view showing a golf ball according to Comparative Example 3. FIG. 34 is a plan view showing the golf ball of FIG. 33. FIG. 35 is a front view showing a golf ball according to Comparative Example 4. FIG. 36 is a plan view showing the golf ball of FIG. 35.

Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

The golf ball 2 shown in FIG. 1 includes a spherical core 4, an intermediate layer 6 located outside the core 4, and a cover 8 located outside the intermediate layer 6. The golf ball 2 has a large number of dimples 10 on its surface. The portion of the surface of the golf ball 2 other than the dimples 10 is the land 12. The golf ball 2 has a paint layer and a mark layer on the outside of the cover-8, but the illustration of these layers is omitted. The golf ball 2 may have another layer between the core 4 and the intermediate layer 6. The golf ball 2 may have another layer between the intermediate layer 6 and the cover-8.

The diameter of the golf ball 2 is preferably 40 mm or more and 45 mm or less. A diameter of 42.67 mm or more is particularly preferred from the perspective of meeting the standards of the United States Golf Association (USGA). From the viewpoint of suppressing air resistance, the diameter is more preferably 44 mm or less, and particularly preferably 42.80 mm or less.

The mass of the golf ball 2 is preferably 40 g or more and 50 g or less. From the viewpoint that a large inertia can be obtained, the mass is more preferably 44 g or more, and particularly preferably 45.00 g or more. From the viewpoint that the USGA standard is satisfied, the mass is particularly preferably 45.93 g or less.

The core 4 is formed by cross-linking the rubber composition. Preferred base rubbers include polybutadiene, polyisoprene, styrene-butadiene copolymers, ethylene-propylene-diene copolymers and natural rubbers. From the viewpoint of resilience performance, polybutadiene is preferable. When polybutadiene and other rubbers are used in combination, it is preferable that polybutadiene is the main component. Specifically, the ratio of polybutadiene to the total base rubber is preferably 50% by mass or more, and particularly preferably 80% by mass or more. Polybutadiene having a cis-1,4 bond ratio of 80% or more is particularly preferable.

The rubber composition of the core 4 preferably contains a co-crosslinking agent. A preferred co-crosslinking agent from the viewpoint of resilience performance is a monovalent or divalent metal salt of α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms. Preferred co-crosslinking agents include zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. From the viewpoint of flight performance on driver shots, zinc acrylate and zinc methacrylate are particularly preferable.

The rubber composition may contain an α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms and a metal oxide. Both react in the rubber composition to give a salt. This salt functions as a co-crosslinking agent. Preferred α, β-unsaturated carboxylic acids include acrylic acid and methacrylic acid. Preferred metal oxides include zinc oxide and magnesium oxide.

From the viewpoint of flight performance on a driver shot, the amount of the co-crosslinking agent is preferably 10 parts by mass or more, and particularly preferably 15 parts by mass or more with respect to 100 parts by mass of the base rubber. From the viewpoint of a soft shot feeling in putting, this amount is preferably 50 parts by mass or less, and particularly preferably 45 parts by mass or less.

Preferably, the rubber composition of the core 4 contains an organic peroxide. The organic peroxide functions as a cross-linking initiator. The organic peroxide contributes to the resilience performance of the golf ball 2. Suitable organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t-butyl). Peroxy) Hexane and di-t-butyl peroxide are exemplified. A particularly versatile organic peroxide is dicumyl peroxide.

From the viewpoint of flight performance on a driver shot, the amount of organic peroxide is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and 0.5 part by mass with respect to 100 parts by mass of the base rubber. More than a portion is particularly preferable. From the viewpoint of a soft shot feeling in putting, this amount is preferably 3.0 parts by mass or less, more preferably 2.8 parts by mass or less, and particularly preferably 2.5 parts by mass or less.

Preferably, the rubber composition of the core 4 contains an organic sulfur compound. Organic sulfur compounds include naphthalenethiol compounds, benzenethiol compounds and disulfide compounds.

As naphthalenethiol compounds, 1-naphthalenethiol, 2-naphthalenethiol, 4-chloro-1-naphthalenethiol, 4-bromo-1-naphthalenethiol, 1-chloro-2-naphthalenethiol, 1-bromo-2-naphthalene Examples thereof include thiol, 1-fluoro-2-naphthalenethiol, 1-cyano-2-naphthalenethiol and 1-acetyl-2-naphthalenethiol.

Examples of benzenethiol compounds include benzenethiol, 4-chlorobenzenethiol, 3-chlorobenzenethiol, 4-bromobenzenethiol, 3-bromobenzenethiol, 4-fluorobenzenethiol, 4-iodobenzenethiol, and 2,5-dichlorobenzenethiol. , 3,5-Dichlorobenzene thiol, 2,6-dichlorobenzene thiol, 2,5-dibromobenzene thiol, 3,5-dibromobenzene thiol, 2-chloro-5-bromobenzene thiol, 2,4,6-tri Chlorobenzene thiol, 2,3,4,5,6-pentachlorobenzene thiol, 2,3,4,5,6-pentafluorobenzene thiol, 4-cyanobenzene thiol, 2-cyanobenzene thiol, 4-nitrobenzene thiol and 2 -Nitrobenzene thiols are exemplified.

As disulfide compounds, 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) Examples thereof include 5,6-pentachlorophenyl) disulfide and bis (2,3,4,5,6-pentabromophenyl) disulfide.

From the viewpoint of flight performance on a driver shot, the amount of the organic sulfur compound is preferably 0.1 part by mass or more, particularly preferably 0.2 part by mass or more with respect to 100 parts by mass of the base rubber. From the viewpoint of a soft shot feeling in putting, this amount is preferably 1.5 parts by mass or less, more preferably 1.0 part by mass or less, and particularly preferably 0.8 parts by mass or less. Two or more organic sulfur compounds may be used in combination. It is preferable that a naphthalenethiol-based compound and a disulfide-based compound are used in combination.

Preferably, the rubber composition of the core 4 comprises a carboxylic acid or a carboxylic acid salt. In the core 4 containing a carboxylic acid or a carboxylic acid salt, the hardness near the center is small. The core 4 has an outer rigid inner flexible structure. The spin speed when the golf ball 2 having the core 4 is hit by the driver is small. With the golf ball 2 having a small spin speed, a large flight distance can be obtained. Benzoic acid is exemplified as a preferable carboxylic acid. Zinc octanate and zinc stearate are exemplified as preferred carboxylates. It is particularly preferred that the rubber composition comprises benzoic acid. The amount of the carboxylic acid and the carboxylic acid salt is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the base rubber.

The rubber composition of the core 4 may contain a filler for the purpose of adjusting the specific gravity and the like. Suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. The amount of filler is appropriately determined so that the intended specific gravity of the core 4 is achieved. The rubber composition may contain appropriate amounts of various additives such as sulfur, anti-aging agents, colorants, plasticizers and dispersants. The rubber composition may include crosslinked rubber powder or synthetic resin powder.

The diameter of the core 4 is preferably 38.0 mm or more. The golf ball 2 having the core 4 having a diameter of 38.0 mm or more is excellent in flight performance on a driver shot. From this point of view, the diameter is more preferably 38.5 mm or more, and particularly preferably 39.5 mm or more. From the viewpoint that the intermediate layer 6 and the cover-8 can have a sufficient thickness, the diameter is preferably 41.0 mm or less, and particularly preferably 40.5 mm or less.

The mass of the core 4 is preferably 10 g or more and 40 g or less. The cross-linking temperature of the core 4 is 140 ° C. or higher and 180 ° C. or lower. The cross-linking time of the core 4 is 10 minutes or more and 60 minutes or less. The core 4 may have two or more layers. The core 4 may have ribs on its surface. The core 4 may be hollow.

In this golf ball 2, the difference (Hs-Ho) between the hardness Hs on the surface of the core 4 and the hardness Ho at the center of the core 4 exceeds 15. In other words, the golf ball 2 satisfies the following mathematical formula (i).
Hs-Ho> 15 (i)
The core 4 satisfying the above formula (i) has a so-called outer rigid inner flexible structure. When the golf ball 2 having the core 4 is hit by the driver, the spin is suppressed. When the golf ball 2 having the core 4 is hit by a driver, a large launch angle is obtained.

For driver shots, an appropriate trajectory height and an appropriate flight time are required. The golf ball 2, which achieves ballistic height and flight time at a large spin speed, has a small run after falling. A golf ball 2 that achieves ballistic height and flight time at a large launch angle has a large run after falling. From the viewpoint of flight distance, a golf ball 2 that achieves ballistic height and flight time at a large launch angle is preferable. As described above, the core 4 having the outer rigid inner flexible structure can contribute to a large launch angle and a small spin velocity. The golf ball 2 having the core 4 is excellent in flight performance.

From the viewpoint of flight performance, the difference (Hs-Ho) is preferably 17 or more, and particularly preferably 19 or more. From the viewpoint of easiness of manufacturing the core 4, the difference (Hs-Ho) is preferably 50 or less, and particularly preferably 45 or less.

From the viewpoint of flight performance on driver shots, the central hardness Ho is preferably 40 or more, more preferably 43 or more, and particularly preferably 46 or more. From the viewpoint of spin suppression and the shot feeling in putting, the hardness Ho is preferably 60 or less, more preferably 57 or less, and particularly preferably 54 or less.

Hardness Ho is measured by a Shore C-type hardness tester attached to an automatic hardness tester (trade name "Digitest II" manufactured by H. Burleys). This hardness tester is pressed against the center of the cross section of the hemisphere obtained by cutting the golf ball 2. The measurement is made in an environment of 23 ° C.

From the viewpoint of spin suppression, the surface hardness Hs is preferably 70 or more, more preferably 72 or more, and particularly preferably 74 or more. From the viewpoint of the durability of the golf ball 2, the hardness Hs is preferably 90 or less, more preferably 88 or less, and particularly preferably 86 or less.

Hardness Hs is measured by a Shore C type hardness tester attached to an automatic hardness tester (trade name "Digitest II" manufactured by H. Burleys). This hardness tester is pressed against the surface of the core 4. The measurement is made in an environment of 23 ° C.

The intermediate layer 6 is located between the core 4 and the cover-8. The intermediate layer 6 is molded from a thermoplastic resin composition. Examples of the base polymer of this resin composition include an ionomer resin, a thermoplastic polyester elastomer, a thermoplastic polyamide elastomer, a thermoplastic polyurethane elastomer, a thermoplastic polyolefin elastomer, and a thermoplastic polystyrene elastomer. In particular, ionomer resin is preferable. Ionomer resin has high elasticity. The golf ball 2 having the intermediate layer 6 containing the ionomer resin is excellent in flight performance on driver shots.

Ionomer resin and other resins may be used in combination. When used in combination, ionomer resin is the main component of the base polymer from the viewpoint of flight performance on driver shots. The ratio of the ionomer resin to the total base polymer is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 85% or more.

Preferred ionomer resins include binary copolymers of α-olefins and α, β-unsaturated carboxylic acids having 3 or more and 8 or less carbon atoms. Preferred binary copolymers include 80% by mass or more and 90% by mass or less of α-olefins and 10% by mass or more and 20% by mass or less of α, β-unsaturated carboxylic acids. This binary copolymer is excellent in resilience performance. As other preferable ionomer resins, a ternary copolymer of an α-olefin, an α, β-unsaturated carboxylic acid having 3 or more and 8 or less carbon atoms and an α, β-unsaturated carboxylic acid ester having 2 or more and 22 or less carbon atoms Examples include copolymers. Preferred ternary copolymers are 70% by mass or more and 85% by mass or less of α-olefin, 5% by mass or more and 30% by mass or less of α, β-unsaturated carboxylic acid, and 1% by mass or more and 25% by mass or less. Includes α, β-unsaturated carboxylic acid esters. This ternary copolymer is excellent in resilience performance. In the binary copolymer and the ternary copolymer, the preferred α-olefins are ethylene and propylene, and the preferred α, β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. A particularly preferred ionomer resin is a copolymer of ethylene and acrylic acid. A particularly preferred other ionomer resin is a copolymer of ethylene and methacrylic acid.

In the binary copolymer and the ternary copolymer, a part of the carboxyl group is neutralized with a metal ion. Examples of the metal ion for neutralization include sodium ion, potassium ion, lithium ion, zinc ion, calcium ion, magnesium ion, aluminum ion and neodymium ion. Neutralization may be done with two or more metal ions. Particularly suitable metal ions from the viewpoint of flight performance and durability on driver shots are sodium ion, zinc ion, lithium ion and magnesium ion.

As specific examples of ionomer resins, the trade names of Mitsui DuPont Polychemical Co., Ltd. "Himilan 1555", "Himiran 1557", "Himiran 1605", "Himiran 1706", "Himiran 1707", "Himiran 1856", "Himiran 1855", "Hi-Miran AM7311", "Hi-Milan AM7315", "Hi-Milan AM7317", "Hi-Milan AM7329" and "Hi-Milan AM7337"; "Salin 8140", "Salin 8150", "Salin 8940", "Salin 8945", "Salin 9120", "Salin 9150", "Salin 9910", "Salin 9945", "Salin AD8546", "HPF1000" and " HPF2000 ”; and the trade names of Exxon Mobile Chemicals, Inc., “IOTEK7010”, “IOTEK7030”, “IOTEK7510”, “IOTEK7520”, “IOTEK8000” and “IOTEK8030”. Two or more types of ionomer resins may be used in combination.

The resin composition of the intermediate layer 6 may contain a styrene block-containing thermoplastic elastomer. 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 the diene block compound include butadiene, isoprene, 1,3-pentadiene and 2,3-dimethyl-1,3-butadiene. Butadiene and isoprene are preferred. Two or more compounds may be used in combination.

Styrene block-containing thermoplastic elastomers include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-butadiene-styrene block copolymer (SIBS), Includes SBS hydrolyzate, SIS hydrous and SIBS hydrous. Styrene-ethylene-butylene-styrene block copolymers (SEBS) can be mentioned as hydrogenators of SBS. Examples of SIS hydrogenated products include styrene-ethylene-propylene-styrene block copolymer (SEPS). Examples of the hydrogenated product of SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

From the viewpoint of flight performance in driver shots, the content of the styrene component in the styrene block-containing thermoplastic elastomer is preferably 10% by mass or more, more preferably 12% by mass or more, and particularly preferably 15% by mass or more. From the viewpoint of shot feeling in putting, this content is preferably 50% by mass or less, more preferably 47% by mass or less, and particularly preferably 45% by mass or less.

In the present invention, the styrene block-containing thermoplastic elastomer includes an alloy of one or more selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS and SEEPS, and an olefin. It is presumed that the olefin component in this alloy contributes to the improvement of compatibility with other base polymer. This alloy can contribute to the resilience performance of the golf ball 2. An olefin having 2 or more and 10 or less carbon atoms is preferable. Suitable olefins include ethylene, propylene, butene and pentene. Ethylene and propylene are particularly preferred.

As specific examples of polymer alloys, Mitsubishi Chemical Corporation's product names "Lavaron T3221C", "Lavaron T3339C", "Lavaron SJ4400N", "Lavaron SJ5400N", "Lavaron SJ6400N", "Lavaron SJ7400N", "Lavaron SJ8400N", "Lavaron SJ8400N" Examples thereof include "SJ9400N" and "Lavalon SR04". Other specific examples of the styrene block-containing thermoplastic elastomer include the trade name "Epofriend A1010" of Daicel Chemical Industries, Ltd. and the trade name "Septon HG-252" of Kuraray.

From the viewpoint of shot feeling in putting, the ratio of the styrene block-containing thermoplastic elastomer to the total base polymer is preferably 5% by mass or more, more preferably 15% by mass or more, and particularly preferably 20% by mass or more. From the viewpoint of flight performance on a driver shot, this ratio is preferably 70% by mass or less, more preferably 60% by mass or less, and particularly preferably 55% by mass or less.

The resin composition of the intermediate layer 6 may contain a filler for the purpose of adjusting the specific gravity and the like. Suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. This resin composition may contain a powder made of a high specific gravity metal as a filler. Specific examples of high specific gravity metals include tungsten and molybdenum. The amount of filler is appropriately determined so that the intended specific gravity of the intermediate layer 6 is achieved. The resin composition may include a colorant, crosslinked rubber powder or synthetic resin powder. When the hue of the golf ball 2 is white, the typical colorant is titanium dioxide.

The hardness Hm of the intermediate layer 6 is preferably 40 or more and 90 or less. The golf ball 2 having the intermediate layer 6 having a hardness Hm of 40 or more is excellent in flight performance on a driver shot. From this viewpoint, the hardness Hm is more preferably 50 or more, and particularly preferably 55 or more. The golf ball 2 having the intermediate layer 6 having a hardness of 90 or less is excellent in shot feeling in putting. From this viewpoint, the hardness Hm is more preferably 85 or less, and particularly preferably 83 or less. When the golf ball 2 has two or more intermediate layers 6, the hardness of each intermediate layer 6 is preferably within the above range.

Hardness Hm is measured in accordance with the provisions of "ASTM-D 2240-68". Hardness Hm is measured by a Shore C-type hardness tester attached to an automatic hardness tester (trade name "Digitest II" manufactured by H. Burleys). For the measurement, a sheet formed by hot pressing and made of the same material as the intermediate layer 6 and having a thickness of about 2 mm is used. Prior to measurement, the sheet is stored at a temperature of 23 ° C. for 2 weeks. At the time of measurement, three sheets are overlapped.

In this embodiment, the number of intermediate layers 6 is 1. Therefore, the shore C hardness Hm (min) of the layer having the lowest hardness in the intermediate layer 6 is equal to the above-mentioned hardness Hm. The shore C hardness Hm (max) of the layer having the highest hardness among the intermediate layers 6 is equal to the above-mentioned hardness Hm. In this embodiment, the hardness Hm (min) is equal to the hardness Hm (max).

The thickness Tm of the intermediate layer 6 is preferably 0.3 mm or more and 2.5 mm or less. The golf ball 2 having the intermediate layer 6 having a thickness Tm of 0.3 mm or more is excellent in shot feeling in putting. From this viewpoint, the thickness Tm is more preferably 0.5 mm or more, and particularly preferably 0.8 mm or more. The golf ball 2 having the intermediate layer 6 having a thickness Tm of 2.5 mm or less is excellent in flight performance on a driver shot. From this viewpoint, the thickness Tm is more preferably 2.0 mm or less, and particularly preferably 1.8 mm or less. The thickness Tm is measured directly below the land 12. When the golf ball 2 has two or more intermediate layers 6, the thickness of each intermediate layer 6 is preferably within the above range.

Cover-8 is the outermost layer, except for the mark layer and the paint layer. The cover-8 is formed from a resin composition. Preferred base polymers of this resin composition include ionic resin, thermoplastic polyester elastomer, thermoplastic polyamide elastomer, thermoplastic polyurethane elastomer, thermoplastic polyolefin elastomer and thermoplastic polystyrene elastomer. In particular, ionomer resin is preferable. Ionomer resin has high elasticity. The golf ball 2 having the cover 8 containing the ionomer resin is excellent in flight performance on driver shots. The ionomer resin described above for the intermediate layer 6 can be used for the cover-8.

Ionomer resin and other resins may be used in combination. Examples of the resin used in combination with the ionomer resin include polyurethane, polyester, polyamide, polyolefin and polystyrene. When used in combination, ionomer resin is the main component of the base polymer from the viewpoint of flight performance on driver shots. The ratio of the amount of the ionomer resin to the total amount of the base polymer is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

The resin composition of the cover-8 may contain an appropriate amount of a colorant, a filler, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, a fluorescent whitening agent and the like. When the hue of the golf ball 2 is white, the typical colorant is titanium dioxide.

From the viewpoint of flight performance on a driver shot, the shore C hardness Hc of the cover-8 is preferably 76 or more, more preferably 79 or more, and particularly preferably 82 or more. From the viewpoint of shot feeling in putting, the hardness Hc is preferably 97 or less, more preferably 95 or less, and particularly preferably 93 or less.

The hardness Hc of the cover-8 is measured in accordance with the provisions of "ASTM-D 2240-68". Hardness Hc is measured by a Shore C-type hardness tester attached to an automatic hardness tester (trade name "Digitest II" manufactured by H. Burleys). For the measurement, a sheet made of the same material as the cover-8 and having a thickness of about 2 mm, which is formed by a hot press, is used. Prior to measurement, the sheet is stored at a temperature of 23 ° C. for 2 weeks. At the time of measurement, three sheets are overlapped.

From the viewpoint of flight performance on driver shots, the thickness Tc of the cover-8 is preferably 0.5 mm or more, more preferably 0.7 mm or more, and particularly preferably 0.8 mm or more. From the viewpoint of shot feeling in putting, this thickness Tc is preferably 2.0 mm or less, more preferably 1.5 mm or less, and particularly preferably 1.0 mm or less. The thickness Tc is measured directly below the land 12.

A known method such as an injection molding method or a compression molding method can be adopted for forming the cover-8. At the time of molding the cover-8, the dimples 10 are formed by the pimples formed on the cavity surface of the molding die.

The amount of compression deformation Sb of the golf ball 2 is preferably 2.5 mm or more and 4.5 mm or less. The golf ball 2 having a compressive deformation amount Sb of 2.5 mm or more has an excellent shot feeling in putting. From this viewpoint, the compressive deformation amount Sb is preferably 2.7 mm or more, and particularly preferably 2.8 mm or more. The golf ball 2 having a compression deformation amount Sb of 4.5 mm or less is excellent in flight performance on a driver shot. From this viewpoint, the compressive deformation amount Sb is more preferably 4.0 mm or less, and particularly preferably 3.8 mm or less.

A YAMADA type compression tester is used to measure the amount of compression deformation. In this tester, the golf ball 2 is placed on a metal rigid plate. A metal cylinder gradually descends toward the golf ball 2. The golf ball 2 sandwiched between the bottom surface of the cylinder and the rigid plate is deformed. The moving distance of the cylinder from the state where the initial load of 98N is applied to the golf ball 2 to the state where the final load of 1274N is applied is measured. The moving speed of the cylinder until the initial load is applied is 0.83 mm / s. The moving speed of the cylinder from the initial load to the final load is 1.67 mm / s.

In this golf ball 2, the difference (Hc-Hm (min)) between the hardness Hc of the cover-8 and the hardness Hm (min) of the layer having the lowest hardness among the intermediate layers 6 is larger than 20. In other words, the golf ball 2 satisfies the following mathematical formula (ii).
Hc − Hm (min)> 20 (ii)
The spin speed when the golf ball 2 satisfying the above formula (ii) is hit by the driver is small. This golf ball 2 is excellent in flight performance on driver shots. From this viewpoint, the difference (Hc-Hm (min)) is more preferably 22 or more, and particularly preferably 24 or more. From the viewpoint of shot feeling in putting, the difference (Hc-Hm (min)) is preferably 42 or less, more preferably 40 or less, and particularly preferably 38 or less.

In this golf ball 2, the difference (Hm (min) -Ho) between the hardness Hm (min) of the layer having the lowest hardness in the intermediate layer 6 and the center hardness Ho of the core 4 is more than -10 and less than 15. Is. In other words, the golf ball 2 satisfies the following mathematical formula (iii).
-10 <Hm (min) -Ho <15 (iii)
When a golf ball 2 having a difference (Hm (min) − Ho) of more than −10 is hit by a driver, the spin speed is small. This golf ball 2 is excellent in flight performance on driver shots. From this point of view, the difference (Hm (min) -Ho) is more preferably -8 or more, and particularly preferably -6 or more. The golf ball 2 having a difference (Hm (min) −Ho) of less than 15 has an excellent shot feeling in putting. From this point of view, the difference (Hm (min) -Ho) is more preferably 13 or less, and particularly preferably 12 or less.

In this golf ball 2, the difference (Hc-Hs) between the hardness Hc of the cover 8 and the surface hardness Hs of the core 4 is more than 5 and less than 20. In other words, the golf ball 2 satisfies the following mathematical formula (iv).
5 <Hc − Hs <20 (iv)
When a golf ball 2 having a difference (Hc—Hs) of more than 5 is hit by a driver, the spin speed is small. This golf ball 2 is excellent in flight performance on driver shots. From this point of view, the difference (Hc—Hs) is more preferably 6 or more, and particularly preferably 7 or more. The spin speed when the golf ball 2 having a difference (Hc—Hs) of less than 20 is hit by the driver is small. This golf ball 2 is excellent in flight performance on driver shots. From this point of view, the difference (Hc—Hs) is more preferably 19 or less, and particularly preferably 18 or less.

The hardness Hc of the cover-8 is larger than the hardness Hm (max) of the layer having the highest hardness among the intermediate layers 6. When a golf ball 2 having a hardness Hc larger than the hardness Hm (max) is hit by a driver, the spin speed is small. This golf ball 2 is excellent in flight performance on driver shots. From this point of view, the difference (Hc-Hm (max)) is preferably 5 or more, more preferably 15 or more, and particularly preferably 20 or more. From the viewpoint of shot feeling in putting, the difference (Hc-Hm (max)) is preferably 45 or less, more preferably 40 or less, and particularly preferably 38 or less.

The total thickness TT of the intermediate layer 6 and the cover-8 is preferably 2.8 mm or less. The golf ball 2 having a thickness TT of 2.8 mm or less is excellent in shot feeling in putting. From this viewpoint, the thickness TT is more preferably 2.6 mm or less, and particularly preferably 2.4 mm or less. From the viewpoint of the durability of the golf ball 2, the thickness TT is preferably 1.0 mm or more, more preferably 1.4 mm or more, and particularly preferably 1.6 mm or more. In the golf ball 2 having two or more intermediate layers 6, the thickness TT is the sum of the thickness of the cover-8 and the thickness of all the intermediate layers 6.

As shown in FIGS. 2 and 3, the contour of each dimple 10 is a circle. The golf ball 2 includes dimples A having a diameter of 4.40 mm, dimples B having a diameter of 4.30 mm, dimples C having a diameter of 4.15 mm, and dimples D having a diameter of 3.90 mm. It is equipped with dimples E having a diameter of 3.00 mm. The number of types of dimples 10 is 5. The golf ball 2 may have the non-circular dimples 10 in place of or with the circular dimples 10.

The number of dimples A is 60, the number of dimples B is 158, the number of dimples C is 72, the number of dimples D is 36, and the number of dimples E is 12. The total number of dimples 10 is 338. A dimple pattern is formed by these dimples 10 and lands 12.

FIG. 4 shows a cross section of the golf ball 2 along a plane passing through the center of the dimple 10 and the center of the golf ball 2. The vertical direction in FIG. 4 is the depth direction of the dimple 10. What is shown by the alternate long and short dash line 14 in FIG. 4 is a virtual sphere. The surface of the virtual sphere 14 is the surface of the golf ball 2 when the dimples 10 are assumed to be absent. The diameter of the virtual sphere 14 is the same as the diameter of the golf ball 2. The dimple 10 is recessed from the surface of the virtual sphere 14. The land 12 coincides with the surface of the virtual sphere 14. In the present embodiment, the cross-sectional shape of the dimple 10 is substantially an arc. The radius of curvature of this arc is indicated by the symbol CR in FIG.

In FIG. 4, the arrow Dm indicates the diameter of the dimple 10. This diameter Dm is the distance between one contact Ed and the other contact Ed when a common tangent Tg is drawn on both sides of the dimple 10. The contact Ed is also the edge of the dimple 10. The edge Ed defines the contour of the dimple 10.

The diameter Dm of each dimple 10 is preferably 2.0 mm or more and 6.0 mm or less. The dimples 10 having a diameter Dm of 2.0 mm or more contribute to turbulence. The golf ball 2 having the dimples 10 is excellent in flight performance on a driver shot. From this viewpoint, the diameter Dm is more preferably 2.5 mm or more, and particularly preferably 2.8 mm or more. The dimple 10 having a diameter Dm of 6.0 mm or less does not impair the essence of the golf ball 2 that it is substantially a sphere. From this viewpoint, the diameter Dm is more preferably 5.5 mm or less, and particularly preferably 5.0 mm or less.

In the case of the non-circular dimple 10, a circular dimple 10 having the same area as the area of the non-circular dimple 10 is virtualized. The diameter of this virtual circular dimple 10 is considered to be the diameter of the non-circular dimple 10.

In FIG. 4, the double-headed arrow Dp1 indicates the first depth of the dimple 10. This first depth Dp1 is the distance between the deepest part of the dimple 10 and the surface of the virtual sphere 14. In FIG. 4, the double-headed arrow Dp2 indicates the second depth of the dimple 10. This second depth Dp2 is the distance between the deepest part of the dimple 10 and the tangent Tg.

From the viewpoint that the hop of the golf ball 2 is suppressed, the first depth Dp1 of the dimple 10 is preferably 0.10 mm or more, more preferably 0.13 mm or more, and particularly preferably 0.15 mm or more. From the viewpoint of suppressing the drop of the golf ball 2, the first depth Dp1 is preferably 0.65 mm or less, more preferably 0.60 mm or less, and particularly preferably 0.55 mm or less.

The area s of the dimple 10 is the area of the area surrounded by the contour of the dimple 10 when the center of the golf ball 2 is viewed from infinity. In the case of the circular dimple 10, the area S is calculated by the following formula.
S = (Dm / 2) ² * π

In the golf ball 2 shown in FIGS. 2 and 3, the area of the dimple A is 15.20 mm ² , the area of the dimple B is 14.52 mm ² , and the area of the dimple C is 13.53 mm ^2. The area of D is 11.95 mm ² , and the area of dimple E is 7.07 mm ² .

In the present invention, the ratio of the total area S of all dimples 10 to the surface area of the virtual sphere 14 is referred to as an occupancy rate. From the viewpoint of achieving sufficient turbulence, the occupancy rate is preferably 78% or more, more preferably 80% or more, and particularly preferably 82% or more. The occupancy rate is preferably 95% or less. In the golf ball 2 shown in FIGS. 2 and 3, the total area of the dimples 10 is 4695.4 mm ² . Since the surface area of the virtual ball 14 of the golf ball 2 is 5728 mm ² , the occupancy rate is 82.0%.

From the viewpoint that a sufficient occupancy rate is achieved, the total number N of the dimples 10 is preferably 250 or more, more preferably 280 or more, and particularly preferably 300 or more. From the viewpoint that each dimple 10 can contribute to turbulence, the total number N is preferably 450 or less, more preferably 400 or less, and particularly preferably 380 or less.

In the present invention, the "volume V of the dimple 10" means the volume of the portion surrounded by the surface of the virtual sphere 14 and the surface of the dimple 10. The total volume TV of the dimple 10 is preferably 450 mm ³ or more and 750 mm ³ or less. In the golf ball 2 having a total volume TV of 450 mm ³ or more, hops during flight are suppressed. In this respect, the total volume of TV is more preferably 480 mm ³ or more, 500 mm ³ or more is particularly preferable. In the golf ball 2 having a total volume TV of 750 mm ³ or less, the drop during flight is suppressed. In this respect, the total volume of TV is more preferably 730 mm ³ or less, 710 mm ³ or less is particularly preferred.

The golf ball 2 according to the present invention has excellent aerodynamic characteristics. The evaluation method of this aerodynamic characteristic is
(A) A step in which a great circle existing on the surface of the virtual sphere 14 and orthogonal to the axis Ax is assumed.
(B) A step in which two small circles existing on the surface of the virtual sphere 14, orthogonal to the axis Ax, and having an absolute value of the central angle with the great circle of 30 ° are assumed.
(C) A step in which the surface of the golf ball 2 is partitioned by these small circles, and a region of the surface sandwiched between these small circles is specified.
(D) A step in which 30240 points are determined in this region at a central angle of 3 ° in the axial direction and at a central angle of 0.25 ° in the rotation direction.
(E) Step in which the length L1 of the perpendicular line drawn from each point to the axis Ax is calculated (f) The total length of 21 lengths L1 calculated based on the 21 perpendicular lines arranged in the axial direction is totaled. Step where L2 is calculated,
(G) A step in which a Fourier transform is performed on 1440 data groups having a total length of L2 calculated along the rotation direction to obtain a converted data group.
In addition, (h) the step of calculating the peak value and order of the maximum peak of the converted data group is executed. Each step is detailed below.

FIG. 5 is a schematic diagram for explaining this evaluation method. FIG. 5 shows a virtual ball 14 of the golf ball 2. The North Pole is indicated by the symbol NP in FIG. The North Pole NP corresponds to the apex of the cavity surface formed by the upper mold for forming the golf ball 2. The South Pole is indicated by the code SP. The South Pole SP corresponds to the deepest part of the cavity surface formed by the lower mold for forming the golf ball 2. The equator is indicated by the code Eq. The equator Eq allows the virtual sphere 14 to be divided into the Northern Hemisphere NH and the Southern Hemisphere SH.

The latitude of the North Pole NP is 90 ° (degree). The latitude θ of the equator Eq is zero. The latitude of the South Pole SP is -90 °. The counterclockwise direction when the virtual sphere 14 is viewed from the North Pole NP is the positive direction of longitude φ. The minimum value of φ is zero. The maximum value of φ is 360 °. The spherical polar coordinates of the points existing on the surface of the virtual sphere 14 are represented by (θ, φ). In FIG. 5, the point (0,0) is located in front.

In FIG. 5, the first latitude line is indicated by the reference numeral Loa. The latitude φ of the first parallel Loa is both 0 ° and 360 °. The virtual sphere 14 has innumerable parallels. The latitude line having the maximum number of dimples 10 intersecting the center is defined as the first latitude line Loa. In the dimple 10 that intersects the latitude line at the center, the latitude line passes through the area center of gravity of the dimple 10.

In this evaluation method, the first axis Ax1 is assumed. The first axis Ax1 passes through the points Pn1 and Ps1. The points Pn1 and Ps1 exist on the surface of the virtual sphere 14. Point Pn1 is located in the Northern Hemisphere NH. The coordinates of the point Pn1 are (75,270). Point Ps1 is located in the Southern Hemisphere SH. The coordinates of the point Ps1 are (-75, 90). The first axis Ax1 is tilted with respect to the earth's axis. The angle of inclination is 15 °. The earth's axis is a line passing through the North Pole NP and the South Pole SP.

In this evaluation method, the first great circle GC1 existing on the surface of the virtual ball 14 of the golf ball 2 is assumed. The first axis Ax1 is orthogonal to the first great circle GC1. In other words, the first axis Ax1 is orthogonal to the plane including the first great circle GC1. In FIG. 5, the first great circle GC1 is tilted with respect to the equator Eq. The angle of inclination is 15 °. The great circle is a circle that exists on the surface of the virtual sphere 14 and whose diameter is the same as the diameter of the virtual sphere 14.

The golf ball 2 rotates about the first axis Ax1. At the time of this rotation, the peripheral speed of the first great circle GC1 is fast. Therefore, the surface roughness of the golf ball 2 in and around the first great circle GC1 greatly affects the flight performance of the golf ball 2.

In this evaluation method, two small circles C1 and C2 existing on the surface of the virtual sphere 14 and orthogonal to the first axis Ax1 are assumed. In FIG. 6, these small circles C1 and C2 are shown. Each small circle is parallel to the first great circle GC1.

FIG. 7 schematically shows a cross section of a part of the golf ball 2 of FIG. FIG. 7 shows a cross section of the golf ball 2 passing through the center O. The left-right direction in FIG. 7 is the direction of the first axis Ax1. As shown in FIG. 7, the absolute value of the central angle between the small circle C1 and the first great circle GC1 is 30 °. Although not shown, the absolute value of the central angle between the small circle C2 and the first great circle GC1 is also 30 °. The golf ball 2 is divided by these small circles C1 and C2, and a region of the surface of the golf ball 2 sandwiched between these small circles is specified. Since the peripheral speed of the first great circle GC1 is high, the dimples 10 existing in this region have a great influence on the aerodynamic characteristics of the golf ball 2.

The point P (α) in FIG. 7 is a point located on the surface of the golf ball 2 and having a central angle of α ° (degree) with the first great circle GC1. The point F (α) is the foot of the perpendicular line Pe (α) drawn from the point P (α) to the first axis Ax1. The length of the perpendicular line Pe (α) is indicated by the arrow L1 (α). In other words, the length L1 (α) is the distance between the point P (α) and the first axis Ax1. In one cross section, the length L1 (α) is calculated for the 21 points P (α). Specifically, -30 °, -27 °, -24 °, -21 °, -18 °, -15 °, -12 °, -9 °, -6 °, -3 °, 0 °, 3 °. , 6 °, 9 °, 12 °, 15 °, 18 °, 21 °, 24 °, 27 ° and 30 ° for angles α, the length L1 (α) is calculated. Twenty-one lengths L1 (α) are summed to give a total length L2 (mm). The total length L2 is a parameter depending on the shape of the surface in the cross section shown in FIG.

FIG. 8 shows a partial cross section of the golf ball 2. In FIG. 8, the vertical direction of the paper surface is the direction of the first axis Ax1. In FIG. 8, the reference numeral β indicates the rotation angle of the golf ball 2. In the range of 0 ° or more and less than 360 °, the rotation angle β is set in increments of 0.25 °. The total length L2 is calculated for each rotation angle. As a result, a total length L2 of 1440 is obtained along the direction of rotation. These total lengths L2 are a group of data calculated by one rotation of the golf ball 2. This data group is calculated based on 30240 lengths L1.

A graph in which the data group relating to the first axis Ax1 of the golf ball 2 shown in FIGS. 2 and 3 is plotted is shown in FIG. In this graph, the horizontal axis is the rotation angle β, and the vertical axis is the total length L2. A Fourier transform is performed on this data group. The frequency spectrum is obtained by Fourier transform. In other words, the Fourier transform gives the coefficients of the Fourier series represented by the following formula.

The above formula is a combination of two trigonometric functions having different periods. In the above equations, _{a n} and _{b n} are the Fourier coefficients. The size of each component to be synthesized is determined by these Fourier coefficients. Each coefficient is expressed by the following formula.

In this formula, N is the total number of data in the data group, and F _k is the kth value in the data group. The spectrum is represented by the following formula.

A group of transformed data is obtained by Fourier transform. A graph in which the converted data group is plotted is shown in FIG. In this graph, the horizontal axis is the order and the vertical axis is the amplitude. From this graph, the maximum peak is determined. Further, the peak value Pd1 of the maximum peak and the order Fd1 of the maximum peak are determined. The peak value Pd1 and the order Fd1 are numerical values representing aerodynamic characteristics in rotation around the first axis Ax1. In the present embodiment, the peak value Pd1 is 270.2 mm, and the order Fd1 is 33.

FIG. 11 also shows the virtual ball 14 of the golf ball 2. FIG. 11 shows the equatorial line Eq and the meridian Loa having a longitude φ of zero. In FIG. 11, the point (0,0) is located in front. In FIG. 11, what is indicated by the reference numeral Ax2 is the second axis. The second axis Ax2 passes through the points Pn2 and Ps2. The points Pn2 and Ps2 exist on the surface of the virtual sphere 14. The coordinates of the point Pn2 are (60,270). The coordinates of the point Ps2 are (-60,90). The second axis Ax2 is tilted with respect to the earth's axis. The angle of inclination is 30 °.

FIG. 11 shows a second great circle GC2 that exists on the surface of the virtual sphere 14 of the golf ball 2 and whose second axis Ax2 is orthogonal to each other. The second great circle GC2 is tilted with respect to the equator Eq. The angle of inclination is 30 °.

The aerodynamic characteristics of the rotation centered on the second axis Ax2 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the second axis Ax2. The absolute value of the central angle between the small circle C1 and the second great circle GC2 is 30 °. The absolute value of the central angle between the small circle C2 and the second great circle GC2 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the second axis Ax2 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd2 of the maximum peak and the order Fd2 of the maximum peak are determined. The peak value Pd2 and the order Fd2 are numerical values representing the aerodynamic characteristics in rotation around the second axis Ax2. In the present embodiment, the peak value Pd2 is 177.9 mm, and the order Fd2 is 37.

FIG. 12 also shows the virtual ball 14 of the golf ball 2. FIG. 12 shows the equatorial line Eq and the meridian Loa having the longitude φ of zero. In FIG. 12, the point (0,0) is located in front. In FIG. 12, what is indicated by the reference numeral Ax3 is the third axis. The third axis Ax3 passes through the points Pn3 and Ps3. The points Pn3 and Ps3 exist on the surface of the virtual sphere 14. The coordinates of the point Pn3 are (45,270). The coordinates of the point Ps3 are (-45, 90). The third axis Ax3 is tilted with respect to the earth's axis. The angle of inclination is 45 °.

FIG. 12 shows a third great circle GC3 that exists on the surface of the virtual sphere 14 of the golf ball 2 and is orthogonal to the third axis Ax3. The third great circle GC3 is tilted with respect to the equator Eq. The angle of inclination is 45 °.

The aerodynamic characteristics of the rotation centered on the third axis Ax3 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the third axis Ax3. The absolute value of the central angle between the small circle C1 and the third great circle GC3 is 30 °. The absolute value of the central angle between the small circle C2 and the third great circle GC3 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the third axis Ax3 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd3 of the maximum peak and the order Fd3 of the maximum peak are determined. The peak value Pd3 and the order Fd3 are numerical values representing the aerodynamic characteristics in rotation around the third axis Ax3. In this embodiment, the peak value Pd3 is 150.2 mm and the order Fd3 is 37.

FIG. 13 also shows the virtual ball 14 of the golf ball 2. FIG. 13 shows the equatorial line Eq and the meridian Loa having a longitude φ of zero. In FIG. 13, the point (0,0) is located in front. In FIG. 13, what is indicated by the reference numeral Ax4 is the fourth axis. The fourth axis Ax4 passes through the points Pn4 and Ps4. The points Pn4 and Ps4 exist on the surface of the virtual sphere 14. The coordinates of the point Pn4 are (30,270). The coordinates of the point Ps4 are (-30,90). The fourth axis Ax4 is tilted with respect to the earth's axis. The angle of inclination is 60 °.

FIG. 13 shows a fourth great circle GC4 that exists on the surface of the virtual sphere 14 of the golf ball 2 and is orthogonal to the fourth axis Ax4. The fourth great circle GC4 is tilted with respect to the equator Eq. The angle of inclination is 60 °.

The aerodynamic characteristics of the rotation centered on the fourth axis Ax4 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the fourth axis Ax4. The absolute value of the central angle between the small circle C1 and the fourth great circle GC4 is 30 °. The absolute value of the central angle between the small circle C2 and the fourth great circle GC4 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the fourth axis Ax4 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd4 of the maximum peak and the order Fd4 of the maximum peak are determined. The peak value Pd4 and the order Fd4 are numerical values representing aerodynamic characteristics in rotation around the fourth axis Ax4. In the present embodiment, the peak value Pd4 is 316.4 mm, and the order Fd4 is 34.

FIG. 14 also shows the virtual ball 14 of the golf ball 2. FIG. 14 shows the equatorial line Eq and the meridian Loa having a longitude φ of zero. In FIG. 14, the point (0,0) is located in front. In FIG. 14, what is indicated by the reference numeral Ax5 is the fifth axis. The fifth axis Ax5 passes through the points Pn5 and Ps5. The points Pn5 and Ps5 exist on the surface of the virtual sphere 14. The coordinates of the point Pn5 are (15,270). The coordinates of the point Ps5 are (-15,90). The fifth axis Ax5 is tilted with respect to the earth's axis. The angle of inclination is 75 °.

FIG. 14 shows a fifth great circle GC5 that exists on the surface of the virtual sphere 14 of the golf ball 2 and is orthogonal to the fifth axis Ax5. The fifth great circle GC5 is tilted with respect to the equator Eq. The angle of inclination is 75 °.

The aerodynamic characteristics of the rotation centered on the fifth axis Ax5 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the fifth axis Ax5. The absolute value of the central angle between the small circle C1 and the fifth great circle GC5 is 30 °. The absolute value of the central angle between the small circle C2 and the fifth great circle GC5 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the fifth axis Ax5 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd5 of the maximum peak and the order Fd5 of the maximum peak are determined. The peak value Pd5 and the order Fd5 are numerical values representing aerodynamic characteristics in rotation centered on the fifth axis Ax5. In this embodiment, the peak value Pd5 is 190.0 mm and the order Fd5 is 27.

FIG. 15 also shows the virtual ball 14 of the golf ball 2. FIG. 15 shows the equatorial Eq and the meridian Lob having a longitude φ of 90 °. In FIG. 15, the point (0,90) is located in front. In FIG. 15, what is indicated by the reference numeral Ax6 is the sixth axis. The sixth axis Ax6 passes through the points Pn6 and Ps6. The points Pn6 and Ps6 exist on the surface of the virtual sphere 14. The coordinates of the point Pn6 are (75,0). The coordinates of the point Ps6 are (-75,180). The sixth axis Ax6 is tilted with respect to the earth's axis. The angle of inclination is 15 °.

FIG. 15 shows a sixth great circle GC6 that exists on the surface of the virtual sphere 14 of the golf ball 2 and is orthogonal to the sixth axis Ax6. The sixth great circle GC6 is tilted with respect to the equator Eq. The angle of inclination is 15 °.

The aerodynamic characteristics of the rotation centered on the sixth axis Ax6 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the sixth axis Ax6. The absolute value of the central angle between the small circle C1 and the sixth great circle GC6 is 30 °. The absolute value of the central angle between the small circle C2 and the sixth great circle GC6 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the sixth axis Ax6 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd6 of the maximum peak and the order Fd6 of the maximum peak are determined. The peak value Pd6 and the order Fd6 are numerical values representing the aerodynamic characteristics in rotation around the sixth axis Ax6. In this embodiment, the peak value Pd6 is 270.2 mm and the order Fd6 is 33.

FIG. 16 also shows the virtual ball 14 of the golf ball 2. FIG. 16 shows the equatorial Eq and the meridian Lob having a longitude φ of 90 °. In FIG. 16, the point (0,90) is located in front. In FIG. 16, what is indicated by the reference numeral Ax7 is the seventh axis. The seventh axis Ax7 passes through the points Pn7 and Ps7. The points Pn7 and Ps7 exist on the surface of the virtual sphere 14. The coordinates of the point Pn7 are (60,0). The coordinates of the point Ps7 are (-60,180). The seventh axis Ax7 is tilted with respect to the earth's axis. The angle of inclination is 30 °.

FIG. 16 shows a seventh great circle GC7 that exists on the surface of the virtual sphere 14 of the golf ball 2 and is orthogonal to the seventh axis Ax7. The seventh great circle GC7 is tilted with respect to the equator Eq. The angle of inclination is 30 °.

The aerodynamic characteristics of the rotation centered on the seventh axis Ax7 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the seventh axis Ax7. The absolute value of the central angle between the small circle C1 and the seventh great circle GC7 is 30 °. The absolute value of the central angle between the small circle C2 and the seventh great circle GC7 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the 7th axis Ax7 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd7 of the maximum peak and the order Fd7 of the maximum peak are determined. The peak value Pd7 and the order Fd7 are numerical values representing aerodynamic characteristics in rotation around the seventh axis Ax7. In the present embodiment, the peak value Pd7 is 177.9 mm, and the order Fd7 is 37.

FIG. 17 also shows the virtual ball 14 of the golf ball 2. FIG. 17 shows the equatorial Eq and the meridian Lob having a longitude φ of 90 °. In FIG. 17, the point (0,90) is located in front. In FIG. 17, the eighth axis is indicated by the reference numeral Ax8. The eighth axis Ax8 passes through the points Pn8 and Ps8. The points Pn8 and Ps8 exist on the surface of the virtual sphere 14. The coordinates of the point Pn8 are (45.0). The coordinates of the point Ps8 are (-45, 180). The eighth axis Ax8 is tilted with respect to the earth's axis. The angle of inclination is 45 °.

FIG. 17 shows the eighth great circle GC8 that exists on the surface of the virtual sphere 14 of the golf ball 2 and is orthogonal to the eighth axis Ax8. The eighth great circle GC8 is tilted with respect to the equator Eq. The angle of inclination is 45 °.

The aerodynamic characteristics of the rotation centered on the eighth axis Ax8 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the eighth axis Ax8. The absolute value of the central angle between the small circle C1 and the eighth great circle GC8 is 30 °. The absolute value of the central angle between the small circle C2 and the eighth great circle GC8 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the eighth axis Ax8 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd8 of the maximum peak and the order Fd8 of the maximum peak are determined. The peak value Pd8 and the order Fd8 are numerical values representing the aerodynamic characteristics in rotation around the eighth axis Ax8. In the present embodiment, the peak value Pd8 is 150.2 mm, and the order Fd8 is 37.

FIG. 18 also shows the virtual ball 14 of the golf ball 2. FIG. 18 shows the equatorial Eq and the meridian Lob having a longitude φ of 90 °. In FIG. 18, the point (0,90) is located in front. In FIG. 18, what is indicated by the reference numeral Ax9 is the ninth axis. The ninth axis Ax9 passes through the points Pn9 and Ps9. The points Pn9 and Ps9 exist on the surface of the virtual sphere 14. The coordinates of the point Pn9 are (30,0). The coordinates of the point Ps9 are (-30,180). The ninth axis Ax9 is tilted with respect to the earth's axis. The angle of inclination is 60 °.

FIG. 18 shows a ninth great circle GC9 existing on the surface of the virtual sphere 14 of the golf ball 2 and having the ninth axis Ax9 orthogonal to each other. The ninth great circle GC9 is tilted with respect to the equator Eq. The angle of inclination is 60 °.

The aerodynamic characteristics of the rotation centered on the ninth axis Ax9 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the ninth axis Ax9. The absolute value of the central angle between the small circle C1 and the ninth great circle GC9 is 30 °. The absolute value of the central angle between the small circle C2 and the ninth great circle GC9 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the ninth axis Ax9 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd9 of the maximum peak and the order Fd9 of the maximum peak are determined. The peak value Pd9 and the order Fd9 are numerical values representing aerodynamic characteristics in rotation centered on the ninth axis Ax9. In the present embodiment, the peak value Pd9 is 316.4 mm, and the order Fd9 is 34.

FIG. 19 also shows the virtual ball 14 of the golf ball 2. FIG. 19 shows the equatorial Eq and the meridian Lob having a longitude φ of 90 °. In FIG. 19, the point (0,90) is located in front. In FIG. 19, reference numeral Ax10 is the tenth axis. The tenth axis Ax10 passes through the points Pn10 and Ps10. The points Pn10 and Ps10 exist on the surface of the virtual sphere 14. The coordinates of the point Pn10 are (15.0). The coordinates of the point Ps10 are (-15,180). The tenth axis Ax10 is tilted with respect to the earth's axis. The angle of inclination is 75 °.

FIG. 19 shows a tenth great circle GC10 existing on the surface of the virtual sphere 14 of the golf ball 2 and having the tenth axis Ax10 orthogonal to each other. The tenth great circle GC10 is tilted with respect to the equator Eq. The angle of inclination is 75 °.

The aerodynamic characteristics of the rotation centered on the tenth axis Ax10 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the tenth axis Ax10. The absolute value of the central angle between the small circle C1 and the tenth great circle GC10 is 30 °. The absolute value of the central angle between the small circle C2 and the tenth great circle GC10 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the tenth axis Ax10 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd10 of the maximum peak and the order Fd10 of the maximum peak are determined. The peak value Pd10 and the order Fd10 are numerical values representing aerodynamic characteristics in rotation centered on the tenth axis Ax10. In the present embodiment, the peak value Pd10 is 190.0 mm, and the order Fd10 is 27.

FIG. 20 also shows the virtual ball 14 of the golf ball 2. FIG. 20 shows the equator Eq and the meridian Loc having a longitude φ of 180 °. In FIG. 20, the point (0,180) is located in front. In FIG. 20, what is indicated by reference numeral Ax11 is the eleventh axis. The eleventh axis Ax11 passes through the points Pn11 and Ps11. The points Pn11 and Ps11 exist on the surface of the virtual sphere 14. The coordinates of the point Pn11 are (75,90). The coordinates of the point Ps11 are (-75,270). The eleventh axis Ax11 is tilted with respect to the earth's axis. The angle of inclination is 15 °.

FIG. 20 shows the eleven great circle GC11 existing on the surface of the virtual sphere 14 of the golf ball 2 and having the eleventh axis Ax11 orthogonal to each other. The eleventh great circle GC11 is tilted with respect to the equator Eq. The angle of inclination is 75 °.

The aerodynamic characteristics of the rotation centered on the eleventh axis Ax11 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the eleventh axis Ax11. The absolute value of the central angle between the small circle C1 and the eleventh great circle GC11 is 30 °. The absolute value of the central angle between the small circle C2 and the eleventh great circle GC11 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the eleventh axis Ax11 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd11 of the maximum peak and the order Fd11 of the maximum peak are determined. The peak value Pd11 and the order Fd11 are numerical values representing the aerodynamic characteristics in rotation around the eleventh axis Ax11. In this embodiment, the peak value Pd11 is 270.2 mm and the order Fd11 is 33.

FIG. 21 also shows the virtual ball 14 of the golf ball 2. FIG. 21 shows the equator Eq and the meridian Loc having a longitude φ of 180 °. In FIG. 21, the point (0,180) is located in front. In FIG. 21, what is indicated by reference numeral Ax12 is the twelfth axis. The twelfth axis Ax12 passes through the points Pn12 and Ps12. The points Pn12 and Ps12 exist on the surface of the virtual sphere 14. The coordinates of the point Pn12 are (60, 90). The coordinates of the point Ps12 are (-60,270). The twelfth axis Ax12 is tilted with respect to the earth's axis. The angle of inclination is 30 °.

FIG. 21 shows a 12th great circle GC12 that exists on the surface of the virtual sphere 14 of the golf ball 2 and has the twelfth axis Ax12 orthogonal to each other. The twelfth great circle GC12 is tilted with respect to the equator Eq. The angle of inclination is 60 °.

The aerodynamic characteristics of the rotation centered on the twelfth axis Ax12 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the twelfth axis Ax12. The absolute value of the central angle between the small circle C1 and the twelfth great circle GC12 is 30 °. The absolute value of the central angle between the small circle C2 and the twelfth great circle GC12 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the twelfth axis Ax12 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd12 of the maximum peak and the order Fd12 of the maximum peak are determined. The peak value Pd12 and the order Fd12 are numerical values representing aerodynamic characteristics in rotation around the twelfth axis Ax12. In the present embodiment, the peak value Pd12 is 177.9 mm, and the order Fd12 is 37.

FIG. 22 also shows the virtual ball 14 of the golf ball 2. FIG. 22 shows the equatorial line Eq and the meridian Loc having a longitude φ of 180 °. In FIG. 22, the point (0,180) is located in front. In FIG. 22, the thirteenth axis is indicated by the reference numeral Ax13. The thirteenth axis Ax13 passes through the points Pn13 and Ps13. The points Pn13 and Ps13 exist on the surface of the virtual sphere 14. The coordinates of the point Pn13 are (45,90). The coordinates of the point Ps13 are (-45,270). The thirteenth axis Ax13 is tilted with respect to the earth's axis. The angle of inclination is 45 °.

FIG. 22 shows the thirteenth great circle GC13 that exists on the surface of the virtual sphere 14 of the golf ball 2 and is orthogonal to the thirteenth axis Ax13. The thirteenth great circle GC13 is tilted with respect to the equator Eq. The angle of inclination is 45 °.

The aerodynamic characteristics of the rotation centered on the thirteenth axis Ax13 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the thirteenth axis Ax13. The absolute value of the central angle between the small circle C1 and the thirteenth great circle GC13 is 30 °. The absolute value of the central angle between the small circle C2 and the thirteenth great circle GC13 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the thirteenth axis Ax13 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd13 of the maximum peak and the order Fd13 of the maximum peak are determined. The peak value Pd13 and the order Fd13 are numerical values representing aerodynamic characteristics in rotation centered on the thirteenth axis Ax13. In the present embodiment, the peak value Pd13 is 150.2 mm, and the order Fd13 is 37.

FIG. 23 also shows the virtual ball 14 of the golf ball 2. FIG. 23 shows the equator Eq and the meridian Loc having a longitude φ of 180 °. In FIG. 23, the point (0,180) is located in front. In FIG. 23, the fourteenth axis is indicated by the reference numeral Ax14. The fourteenth axis Ax14 passes through the points Pn14 and Ps14. The points Pn14 and Ps14 are present on the surface of the virtual sphere 14. The coordinates of the point Pn14 are (30,90). The coordinates of the point Ps14 are (-30,270). The fourteenth axis Ax14 is tilted with respect to the earth's axis. The angle of inclination is 60 °.

FIG. 23 shows the 14th great circle GC14 that exists on the surface of the virtual sphere 14 of the golf ball 2 and is orthogonal to the 14th axis Ax14. The 14th great circle GC14 is tilted with respect to the equator Eq. The angle of inclination is 60 °.

The aerodynamic characteristics of the rotation centered on the fourteenth axis Ax14 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the fourteenth axis Ax14. The absolute value of the central angle between the small circle C1 and the 14th great circle GC14 is 30 °. The absolute value of the central angle between the small circle C2 and the fourteenth great circle GC14 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the fourteenth axis Ax14 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd14 of the maximum peak and the order Fd14 of the maximum peak are determined. The peak value Pd14 and the order Fd14 are numerical values representing aerodynamic characteristics in rotation centered on the fourteenth axis Ax14. In the present embodiment, the peak value Pd14 is 316.4 mm, and the order Fd14 is 34.

FIG. 24 also shows the virtual ball 14 of the golf ball 2. FIG. 24 shows the equator Eq and the meridian Loc having a longitude φ of 180 °. In FIG. 24, the point (0,180) is located in front. In FIG. 24, the fifteenth axis is indicated by the reference numeral Ax15. The fifteenth axis Ax15 passes through the points Pn15 and Ps15. The points Pn15 and Ps15 exist on the surface of the virtual sphere 14. The coordinates of the point Pn15 are (15,90). The coordinates of the point Ps15 are (-15,270). The fifteenth axis Ax15 is tilted with respect to the earth's axis. The angle of inclination is 75 °.

FIG. 24 shows the fifteenth great circle GC15 that exists on the surface of the virtual sphere 14 of the golf ball 2 and is orthogonal to the fifteenth axis Ax15. The 15th great circle GC15 is tilted with respect to the equatorial Eq. The angle of inclination is 75 °.

The aerodynamic characteristics of the rotation centered on the fifteenth axis Ax15 are evaluated in the same manner as the rotation centered on the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation around the fifteenth axis Ax15. The absolute value of the central angle between the small circle C1 and the fifteenth great circle GC15 is 30 °. The absolute value of the central angle between the small circle C2 and the fifteenth great circle GC15 is also 30 °. The total length L2 of 1440 is calculated in the region of the surface of the golf ball 2 sandwiched between these small circles. In other words, the data group for the fifteenth axis Ax15 is calculated. Fourier transform is performed on this data group, and the transformed data group is obtained. From the graph on which the converted data group is plotted, the peak value Pd15 of the maximum peak and the order Fd15 of the maximum peak are determined. The peak value Pd15 and the order Fd15 are numerical values representing aerodynamic characteristics in rotation centered on the fifteenth axis Ax15. In this embodiment, the peak value Pd15 is 190.0 mm and the order Fd15 is 27.

With this evaluation method,
(1) The first axis Ax1 passing through the point Pn1 whose coordinates are (75,270) and the point Ps1 whose coordinates are (-75,90),
(2) The second axis Ax2, which passes through the point Pn2 whose coordinates are (60,270) and the point Ps2 whose coordinates are (-60,90).
(3) Third axis Ax3, which passes through the point Pn3 whose coordinates are (45,270) and the point Ps3 whose coordinates are (-45,90).
(4) Fourth axis Ax4, which passes through the point Pn4 whose coordinates are (30,270) and the point Ps4 whose coordinates are (-30,90).
(5) The fifth axis Ax5, which passes through the point Pn5 whose coordinates are (15,270) and the point Ps5 whose coordinates are (-15,90).
(6) The sixth axis Ax6, which passes through the point Pn6 whose coordinates are (75,0) and the point Ps6 whose coordinates are (-75,180).
(7) The seventh axis Ax7, which passes through the point Pn7 whose coordinates are (60,0) and the point Ps7 whose coordinates are (-60,180).
(8) The eighth axis Ax8, which passes through the point Pn8 whose coordinates are (45,0) and the point Ps8 whose coordinates are (-45,180).
(9) Ninth axis Ax9, which passes through the point Pn9 whose coordinates are (30,0) and the point Ps9 whose coordinates are (-30,180).
(10) The tenth axis Ax10, which passes through the point Pn10 whose coordinates are (15.0) and the point Ps10 whose coordinates are (-15,180).
(11) The eleventh axis Ax11, which passes through the point Pn11 whose coordinates are (75,90) and the point Ps11 whose coordinates are (-75,270).
(12) The twelfth axis Ax12, which passes through the point Pn12 whose coordinates are (60,90) and the point Ps12 whose coordinates are (-60,270).
(13) The thirteenth axis Ax13, which passes through the point Pn13 whose coordinates are (45,90) and the point Ps13 whose coordinates are (-45,270).
(14) The fourteenth axis Ax14, which passes through the point Pn14 whose coordinates are (30,90) and the point Ps14 whose coordinates are (-30,270).
And (15) the fifteenth axis Ax15 passing through the point Pn15 whose coordinates are (15,90) and the point P15s whose coordinates are (-15,270).
Steps (a)-(h) are executed for each of the 15 axes Ax. As a result, the peak value of 15 (Pd1-Pd15) and the order of 15 (Fd1-Fd15) are calculated.

The smallest of the 15 peak values (Pd1-Pd15) are Pd3, Pd8 and Pd13. The minimum value of the peak value Pd is 150.2 mm. According to the knowledge obtained by the present inventor, the minimum value is preferably 95 mm or more. In the golf ball 2 having a minimum value of 95 mm or more, a sufficient dimple effect can be exhibited at the time of rotation based on any axis Ax. When the golf ball 2 is hit by a driver, the flight distance is large. From this viewpoint, the minimum value of the peak value Pd is more preferably 120 mm or more, and particularly preferably 140 mm or more.

The largest of the 15 peak values (Pd1-Pd15) are Pd4, Pd9 and Pd14. The maximum value of the peak value Pd is 316.4 mm. According to the knowledge obtained by the present inventor, the maximum value is preferably 500 mm or less. The golf ball 2 having a maximum value of 500 mm or less is excellent in aerodynamic characteristics. When the golf ball 2 is hit by a driver, the flight distance is large. From this viewpoint, the maximum value of the peak value Pd is more preferably 400 mm or less, and particularly preferably 330 mm or less.

The average value of the peak values (Pd1-Pd15) of 15 is preferably 200 mm or more. The golf ball 2 having an average value of 200 mm or more has excellent aerodynamic characteristics. When the golf ball 2 is hit by a driver, the flight distance is large. From this viewpoint, the average value is more preferably 210 mm or more, and particularly preferably 220 mm or more. The average value is preferably 300 mm or less, and particularly preferably 230 mm or less. In this embodiment, the average value is 220.9 mm.

The smallest of the 15 orders (Fd1-Fd15) are Fd5, Fd10 and Fd15. The minimum value of the order Fd is 27. According to the findings obtained by the present inventor, the minimum value is preferably 27 or more. The golf ball 2 having a minimum value of 27 or more is excellent in aerodynamic characteristics. When the golf ball 2 is hit by a driver, the flight distance is large.

The largest of the 15 orders (Fd1-Fd15) are Fd2, Fd3, Fd7, Fd8, Fd12 and Fd13. The maximum value of the order Fd is 37. According to the findings obtained by the present inventor, the maximum value is preferably 37 or less. The golf ball 2 having a maximum value of 37 or less is excellent in aerodynamic characteristics. When the golf ball 2 is hit by a driver, the flight distance is large.

The average value of the 15th order (Fd1-Fd15) is preferably 30 or more and 34 or less. The golf ball 2 whose average value is within this range is excellent in aerodynamic characteristics. When the golf ball 2 is hit by a driver, the flight distance is large. In this embodiment, the average value is 33.6.

In this method, the golf ball 2 is evaluated by the peak value Pd of 15 and the order Fd of 15 based on the axis Ax of 15. By this method, the aerodynamic characteristics of the golf ball 2 can be objectively evaluated.

Hereinafter, the effects of the present invention will be clarified by Examples, but the present invention should not be construed in a limited manner based on the description of these Examples.

[Example 1]
100 parts by mass of high cis polybutadiene (JSR trade name "BR-730"), 25.5 parts by mass of zinc acrylate, 12 parts by mass of zinc oxide, appropriate amount of barium sulfate, 0.9 parts by mass of disulfide Peroxide, 0.5 parts by mass of diphenyl disulfide, 0.1 parts by mass of 2-naphthalenethiol and 2.0 parts by mass of benzoic acid were kneaded to obtain a rubber composition A. The rubber composition A was put into a mold composed of an upper mold and a lower mold both having a hemispherical cavity, and heated at 160 ° C. for 20 minutes to obtain a core having a diameter of 38.6 mm. The amount of barium sulfate was adjusted so that a core having a predetermined mass was obtained.

26 parts by mass of ionomer resin (the above-mentioned "Himilan AM7337"), 26 parts by mass of another ionomer resin (the above-mentioned "Himilan AM7329"), 48 parts by mass of a styrene block-containing thermoplastic elastomer (the above-mentioned "Lavalon T3221C") 4, 4 parts by mass of titanium dioxide and 0.2 parts by mass of a light stabilizer (trade name "JF-90" of Johoku Chemical Industry Co., Ltd.) were kneaded with a twin-screw kneading extruder to obtain a resin composition (a). .. This resin composition (a) was coated around the core by an injection molding method to form an intermediate layer. The thickness of this intermediate layer was 1.0 mm.

55 parts by mass of ionomer resin (the above-mentioned "Himilan AM7329"), 45 parts by mass of other ionomer resin (the above-mentioned "Himilan 1555"), 4 parts by mass of titanium dioxide and 0.2 parts by mass of a light stabilizer (Johoku). The trade name "JF-90" of Chemical Industry Co., Ltd.) was kneaded with a twin-screw kneading extruder to obtain a resin composition (e). A sphere composed of a core and an intermediate layer was put into a final mold consisting of an upper mold and a lower mold, each having a hemispherical cavity and having a large number of pimples on the cavity surface. The resin composition (e) was coated around the intermediate layer by an injection molding method to form a cover. The thickness of this cover was 1.05 mm. Dimples having an inverted shape of the pimples were formed on the cover.

A clear paint based on a two-component curable polyurethane was applied around the cover to obtain a golf ball of Example 1 having a diameter of about 42.7 mm and a mass of about 45.6 g. Details of the dimple specification I of this golf ball are shown in Tables 4, 6 and 8 below.

[Examples 2-3 and Comparative Examples 1-4]
The golf balls of Examples 2-3 and Comparative Examples 1-4 were obtained in the same manner as in Example 1 except that the dimple specifications were as shown in Tables 10 and 11 below. Details of the dimple specifications are shown in Table 4-9 below.

[Example 4-7 and Comparative Example 5-10]
Golf balls of Example 4-7 and Comparative Example 5-10 were obtained in the same manner as in Example 1 except that the specifications of the core, the intermediate layer and the cover were as shown in Table 11-13 below. Details of the core specifications are shown in Table 1-2 below. Details of the intermediate layer and cover specifications are shown in Table 3 below.

[Example 9]
100 parts by mass of high cis polybutadiene (JSR trade name "BR-730"), 22.5 parts by mass of zinc acrylate, 12 parts by mass of zinc oxide, appropriate amount of barium sulfate, 0.9 parts by mass of disulfide Peroxide, 0.5 parts by mass of diphenyl disulfide, 0.1 parts by mass of 2-naphthalenethiol and 2.0 parts by mass of benzoic acid were kneaded to obtain a rubber composition B. The rubber composition B was put into a mold composed of an upper mold and a lower mold both having a hemispherical cavity, and heated at 160 ° C. for 20 minutes to obtain a core having a diameter of 36.6 mm. The amount of barium sulfate was adjusted so that a core having a predetermined mass was obtained.

26 parts by mass of ionomer resin (the above-mentioned "Himilan AM7337"), 26 parts by mass of another ionomer resin (the above-mentioned "Himilan AM7329"), 48 parts by mass of a styrene block-containing thermoplastic elastomer (the above-mentioned "Lavalon T3221C") 4, 4 parts by mass of titanium dioxide and 0.2 parts by mass of a light stabilizer (trade name "JF-90" of Johoku Chemical Industry Co., Ltd.) were kneaded with a twin-screw kneading extruder to obtain a resin composition (a). .. This resin composition (a) was coated around the core by an injection molding method to form a first intermediate layer. The thickness of this first intermediate layer was 1.0 mm.

43 parts by mass of ionomer resin (the above-mentioned "Himilan AM7337"), 40 parts by mass of another ionomer resin (the above-mentioned "Himilan AM7329"), 14 parts by mass of a styrene block-containing thermoplastic elastomer (the above-mentioned "Lavalon T3221C") 4, 4 parts by mass of titanium dioxide and 0.2 parts by mass of a light stabilizer (trade name "JF-90" of Johoku Chemical Industry Co., Ltd.) were kneaded with a twin-screw kneading extruder to obtain a resin composition (c). .. This resin composition (c) was coated around the first intermediate layer by an injection molding method to form a second intermediate layer. The thickness of this second intermediate layer was 1.0 mm.

55 parts by mass of ionomer resin (the above-mentioned "Himilan AM7329"), 45 parts by mass of other ionomer resin (the above-mentioned "Himilan 1555"), 4 parts by mass of titanium dioxide and 0.2 parts by mass of a light stabilizer (Johoku). The trade name "JF-90" of Chemical Industry Co., Ltd.) was kneaded with a twin-screw kneading extruder to obtain a resin composition (e). A sphere composed of a core, a first intermediate layer and a second intermediate layer was put into a final mold consisting of an upper mold and a lower mold, each having a hemispherical cavity and having a large number of pimples on the cavity surface. The resin composition (e) was coated around the second intermediate layer by an injection molding method to form a cover. The thickness of this cover was 1.05 mm. Dimples having an inverted shape of the pimples were formed on the cover.

A clear paint based on a two-component curable polyurethane was applied around the cover to obtain a golf ball of Example 8 having a diameter of about 42.7 mm and a mass of about 45.6 g. Details of the dimple specification I of this golf ball are shown in Tables 4, 6 and 8 below.

[Flight test]
A driver (Dunlop Sports' brand name "XXIO PRIME", shaft hardness: R, loft angle: 11.5 °) was attached to the swing machine of Golf Laboratory. The golf ball was hit under the condition that the head speed was 35 m / sec. The ball speed and spin speed immediately after the hit were measured. Furthermore, the flight distance was measured. The flight distance is the distance between the hitting point and the point where the ball is stationary. The average value of the data obtained in the 12 measurements is shown in Table 10-13 below.

[Striking feeling]
Twenty players were made to hit the golf ball with a putter, and the feeling of hitting was heard. The following ratings were given based on the number of golfers who answered that the shot feeling was soft.
A: 16 or more B: 10-15 C: 3-9 D: 2 or less The results are shown in Table 10-13 below.

As shown in Table 10-13, the golf balls of each embodiment are excellent in flight performance in driver shots and shot feeling in putting. From this evaluation result, the superiority of the present invention is clear.

The golf ball according to the present invention is suitable for playing on a golf course, practicing in a driving range, and the like.

2 ... Golf ball 4 ... Core 6 ... Middle layer 8 ... Cover 10 ... Dimple 12 ... Land 14 ... Virtual ball

Claims (4)

A golf ball having a core, one or more intermediate layers located outside the core, and a cover located outside the intermediate layers.
The central shore C hardness Ho and the surface shore C hardness Hs in the core, the shore C hardness Hm (min) of the layer having the lowest hardness among the intermediate layers, and the shore C hardness Hc of the cover are the following mathematical formulas ( i) to (iv) are satisfied,
Hs-Ho> 15 (i)
Hc − Hm (min)> 20 (ii)
-10 <Hm (min) -Ho <15 (iii)
5 <Hc − Hs <20 (iv)
The hardness Hc of the cover is larger than the shore C hardness Hm (max) of the layer having the highest hardness among the intermediate layers.
It also has multiple dimples on its surface,
When the spherical polar coordinates of a point located on the surface of the virtual sphere of the golf ball, where the latitude is θ (degree) and the longitude is φ (degree), are represented by (θ, φ),
(1) The first axis Ax1 passing through the point Pn1 whose coordinates are (75,270) and the point Ps1 whose coordinates are (-75,90),
(2) The second axis Ax2, which passes through the point Pn2 whose coordinates are (60,270) and the point Ps2 whose coordinates are (-60,90).
(3) Third axis Ax3, which passes through the point Pn3 whose coordinates are (45,270) and the point Ps3 whose coordinates are (-45,90).
(4) Fourth axis Ax4, which passes through the point Pn4 whose coordinates are (30,270) and the point Ps4 whose coordinates are (-30,90).
(5) The fifth axis Ax5, which passes through the point Pn5 whose coordinates are (15,270) and the point Ps5 whose coordinates are (-15,90).
(6) The sixth axis Ax6, which passes through the point Pn6 whose coordinates are (75,0) and the point Ps6 whose coordinates are (-75,180).
(7) The seventh axis Ax7, which passes through the point Pn7 whose coordinates are (60,0) and the point Ps7 whose coordinates are (-60,180).
(8) The eighth axis Ax8, which passes through the point Pn8 whose coordinates are (45,0) and the point Ps8 whose coordinates are (-45,180).
(9) Ninth axis Ax9, which passes through the point Pn9 whose coordinates are (30,0) and the point Ps9 whose coordinates are (-30,180).
(10) The tenth axis Ax10, which passes through the point Pn10 whose coordinates are (15.0) and the point Ps10 whose coordinates are (-15,180).
(11) The eleventh axis Ax11, which passes through the point Pn11 whose coordinates are (75,90) and the point Ps11 whose coordinates are (-75,270).
(12) The twelfth axis Ax12, which passes through the point Pn12 whose coordinates are (60,90) and the point Ps12 whose coordinates are (-60,270).
(13) The thirteenth axis Ax13, which passes through the point Pn13 whose coordinates are (45,90) and the point Ps13 whose coordinates are (-45,270).
(14) The fourteenth axis Ax14, which passes through the point Pn14 whose coordinates are (30,90) and the point Ps14 whose coordinates are (-30,270).
And (15) the fifteenth axis Ax15 passing through the point Pn15 whose coordinates are (15,90) and the point Ps15 whose coordinates are (-15,270).
For each of the 15 axes Ax
(A) A step in which a great circle existing on the surface of the virtual sphere and orthogonal to the axis Ax is assumed.
(B) A step in which two small circles existing on the surface of the virtual sphere, orthogonal to the axis Ax, and having an absolute value of the central angle with the great circle of 30 ° are assumed.
(C) A step in which the surface of the golf ball is partitioned by these small circles and the area of the surface sandwiched between these small circles is identified.
(D) A step in which 30240 points are determined in the above region at a central angle of 3 ° in the axial direction and at a central angle of 0.25 ° in the rotation direction.
(E) A step in which the length L1 of the perpendicular line drawn from each point on the axis Ax is calculated.
(F) A step in which 21 lengths L1 calculated based on 21 perpendicular lines arranged in the axial direction are totaled to calculate a total length L2.
(G) A step in which a Fourier transform is performed on 1440 data groups having a total length of L2 calculated along the rotation direction to obtain a converted data group.
(H) The minimum value of the 15 peak values obtained by executing the step of calculating the peak value and the order of the maximum peak of the conversion data group is 95 mm or more.
The minimum value of the order of 15 obtained by executing the above steps (a)-(h) is 27 or more.
The maximum value of the order of 15 obtained by executing the above steps (a)-(h) is 37 or less.
A golf ball having an average value of 15 or more and 34 or less obtained by executing the above steps (a)-(h). The golf ball according to claim 1, wherein the total thickness of the cover and the intermediate layer is 2.8 mm or less. The golf ball according to claim 1 or 2, wherein the average of the 15 peak values obtained by executing the steps (a)-(h) is 200 mm or more. The golf ball according to any one of claims 1 to 3, wherein the total volume of the dimples is 450 mm ³ or more and 750 mm ³ or less.

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